Older blog entries for etbe (starting at number 1123)

Why I Use BTRFS

I’ve just had to do yet another backup/format/restore operation on my workstation due to a BTRFS corruption problem, but as usual I didn’t lose any data. The BTRFS data integrity features work reasonably well even when the filesystem gets into a state where the kernel will only accept a read-only mount.

Given that the BTRFS tag on my blog is mostly about problems with BTRFS I think it’s time that I explain why I use it in spite of the problems before people start to worry about my sanity or competence.

The first thing to note is that BTRFS is fairly resiliant toward errors when mounted in read-only mode. When mounting a filesystem read-write there are a number of ways in which things can break which are often due to kernel code not being able to handle corrupt metadata – I don’t know how much of this is inherent to the design of BTRFS and how much is simply missing features in filesystem error handling. Some of the errors that I have had weren’t entirely the fault of BTRFS, I twice had to do a backup/format/restore of my workstation due to a faulty DIMM corrupting memory (that has the potential to mess up any filesystem), but I still didn’t lose any data AFAIK.

The next thing to note is that I don’t use BTRFS when doing paid sysadmin work. ZFS is a solid and reliable filesystem and it is working really well for my clients while BTRFS has too many issues at the moment. As an aside I’m not interested in any comments about the ZFS license situation from anyone who’s not officially representing Oracle.

I also don’t use BTRFS on systems that I can’t access easily. The servers I have running BTRFS are all within an hour’s drive from home, while driving for an hour on account of a kernel or filesystem error is really annoying it’s not as bad as dealing with a remote server where I have no direct access.

Reasons to Use BTRFS

The benefits of BTRFS right now are snapshots (which are good for a first-line backup) and the basic data integrity features. I’ve found these features to work well in real use.

According to the comparison of Filesystems Wikipedia page ZFS and BTRFS are the only general purpose filesystems (IE for disks not tapes, NVRAM, or a cluster) that support checksums for all data and compression. Given that ZFS license issues will never allow it to be included in the Linux kernel tree it seems clear that BTRFS is the next significant filesystem for Linux. More testing of BTRFS is a good thing, while there are a number of known problems that the developers are working on it seems that more testing is needed now to find corner cases. Also we need a lot of testing to find bugs related to interactions with other software.

I’ve recently filed bug reports against the Debian installer because it can’t install to a BTRFS RAID-1 (fortunately BTRFS supports changing to RAID-1 after installation) and because it doesn’t support formatting an existing BTRFS filesystem (the mkfs program needs a -f option in that case). I also sent in a patch for the magic database used by file(1) to provide more information on BTRFS filesystems (which is in Debian/testing but not Debian/Wheezy). These are the sorts of things you encounter when routinely using software that you don’t necessarily notice in basic testing.

As an aside the Debian installation process failed at the GRUB step when I manually balanced a filesystem to use RAID-1 while the Debian installation was in progress. I didn’t file a bug report because the best advice is to not mess with filesystems while the installer is running. I’ll do a lot more testing of this when the Debian installer supports a BTRFS RAID-1 installation.

A final thing that we need to work on is developing sysadmin best practices and scripts for managing BTRFS filesystems. I’ve done some work on scripts to create snapshots for online backups but there are issues of managing free space etc. But working out how to best manage a new filesystem is something that takes years because there are many corner cases you may only encounter after a system has been running for a long time. So I really wouldn’t want to be in the situation of using a new filesystem on an important server without having practice running it on less important systems, I did that with ZFS and now have a hacky first install that I have to support for years.

Related posts:

  1. BTRFS Status March 2014 I’m currently using BTRFS on most systems that I can...
  2. Starting with BTRFS Based on my investigation of RAID reliability [1] I have...
  3. BTRFS vs LVM For some years LVM (the Linux Logical Volume Manager) has...

Syndicated 2014-05-21 01:18:15 from etbe - Russell Coker

My First Ingress Anomaly

schwag from Ingress Anomaly

Ingress is an Android phone game developed by Google where you have to go to various places to capture “portals” which are based on landmarks or places of note. There’s a sci-fi back story which I haven’t cared much about (my local library has a heap of good sci-fi books I don’t have time to read). But if you are interested in low quality sci-fi you can start with the Youtube channel for Ingress [1]. But the best thing to do is to download the Ingress client program from the Google play store if you have an Android phone [2].

Periodically they have special events in the game called “Anomalies”, which usually involve many people competing to capture a small number of special portals. Usually a portal is fairly easy to capture so a high level player can easily capture a portal in at most a few minutes, but when there is a large group of players defending a portal by replacing the “resonators” as quickly as they are destroyed it becomes more challenging. I’m not going to try to explain this properly as I presume that readers either already know or don’t care. The Wikipedia page about Ingress has more information.

On Saturday there was an Anomaly where the main city was Melbourne. My team (Enlightened) won the event in Australia but apparently the event in the US at the same time was won by the other team (Resistance).

I had hoped that our event would be similar to some of the ones I’ve seen on the “Ingress Report” (a fictional news service on youtube) in which actors from the sci-fi videos about Ingress attended. But unfortunately it seems that the actors stay in the US.

Every player who was registered for the anomaly received a gift pack that contained three cards and a badge. The picture above shows the cards that my wife and I received along with one of our badges. The badges are green for Enlightened and blue for Resistance (the in-game colors) and have three flashing LEDs – the photo has one of the LEDs lit up. The three cards have “passcodes” which can be redeemed for in-game items, the XMP, Power Cubes, and Resonators weren’t that useful (10 not particularly rare items that I could get through 10 minutes of game playing). The “Medal” cards are for in-game badges showing the anomalies that we have played at, but they are “bronze” badges which again aren’t much use as nothing less than silver will help in leveling up.

Overall it was a good experience, we won, had a good after-party (with free snacks and one free drink per person), and the badges are nice. I recommend attending if there’s an event in your area, and note that you don’t need to be a high level player to attend, even L6 players were able to contribute.

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Syndicated 2014-05-19 05:58:21 from etbe - Russell Coker

Mobile Phones and Cognitive Costs

I previously wrote about the case for a Basic Income in Australia [1]. Since then I read an interesting article by Rutger Bregman in the Dutch site The Correspondent discussing the benefit that such Basic Income schemes have given in various places [2], he makes a great case for giving a Basic Income to poor people. However I believe that it should be provided to everyone. I believe that government payments shouldn’t be “means tested” because the proportion of the population who earn more than the cutoff is usually very small (IE it doesn’t save much money), because the money will be recovered from wealthy people in tax, and because the bureaucracy involved in determining who is eligible involves spending tax money to pay bureaucrats and costing everyone time in dealing with the process.

The concept of an Attention Economy has been getting some interest recently. But discussions of it seem to be mostly concerned with the needs of fairly wealthy people, how to advertise to them, how to filter out unwanted ads for them, etc. But the costs in attention can be even worse for people on low incomes or social security because they have many attention costs that could be solved by money. Many common essential purchases (EG soap, basic foods, and purely functional clothes) can become difficult decisions if saving a few dollars is important. The amount of thought involved in buying such items can result in someone who’s not well off having little energy to concentrate on other things. I think that to have an effective social security system we need to consider how much cognitive effort is being required of people who are receiving benefits.

Last month I wrote yet another review of mobile phone plans in Australia [3]. Every time I do this it takes a significant amount of time because the Telcos devise overly complex plans to make it difficult to compare their offerings. It seems that they aim to make their offerings somewhat competitive if you can interpret them but confusing enough to allow many (most?) of their customers to pay needlessly high bills. I could just pick a random telco and pay whatever it takes, spending an extra $10 or $20 per month isn’t such a big deal for me. Even though I advise a number of my relatives on the cheapest phone plan it’s probably only barely saving enough money to be worth the effort, a major motivation for me is being stubborn and not wanting telcos to rip people off.

The Importance of Mobile Phones

A mobile phone seems to be essential for most people. Mobile phones are used for making medical appointments and for applying for work, so in almost every case some of the financial assistance paid to a job seeker or person on a disability pension will go towards mobile phone costs. The aims of the social security benefits seem to clearly involve a phone service. Given that most people who receive social security payments spend some of that money on mobile phone bills the government has a direct financial interest in not having such money wasted on needlessly expensive phone plans. As we also don’t want to have people on social security spending time and attention trying to find the best phone plan it makes sense to have the government help manage this process.

Good communications is regarded as essential to education and economic development. A huge amount of taxpayer money was spent on the NBN (and then wasted by Tony Abbott when he cancelled the original plans) for these benefits.

Good phone access is also an issue of personal safety. While it is possible to call emergency services from a mobile phone that doesn’t have a valid SIM there are probably few people who keep a spare phone charged for that purpose. Also there are a variety of issues that can impact life or health which can best be resolved by calling friends or relatives.

Free Phones

I think that the best solution to these problems is for the government to directly pay mobile phone bills. If we are going to have a Basic Income then the government should make the base payment for mobile phone calls for every resident, if not then the government should make the base payment for everyone who receives any form of social security payment. Obviously the amount of data that could be transferred over a 3G network is greatly in excess of the amount that any plans allow and offering true “unlimited” calling leads to people using mobile phones as baby-monitors, so some limits are necessary. But the government could cheaply pay for a phone plan that exceeds the requirements of most people and then allow anyone who wants more data or calls to pay extra.

Which Plan?

The cheapest all-inclusive mobile phone plan in recent times was Kogan who charged $299 per annum for 6G of data per month and “unlimited” calls. The cheapest current offer for “unlimited” calls seems to be Lebara’s $30 per month offer which includes 2G of data.

My observation is that people who use 3G Internet just for phone use (as opposed to tethering a laptop or providing home Internet), who use a home Wifi network for installing Android programs and don’t play Ingress tend to use a lot less than 1G of data per month. I would use between 400M and 700M per month if I wasn’t playing Ingress and didn’t use my phone as a Wifi access point.

In terms of call volume, 600 minutes a month should be enough to cover the basic needs of most people judging by the number of plans on offer with limits smaller than that.

As a current Lebara offer is $30 per month for “unlimited” calls and 2G of data (and there are similar offers from other telcos), it should be possible for a telco to offer 600 minutes of calls and 1G of data for less than $15 per month. When the government is paying (no bad debts) and many of the users will use much less than the quota such a plan should be profitable at $10 per month or less.

Implementation

The way to implement this would be to start with a tender that has a hard requirement for the minimum amount of service provided. This would include the number of minutes per month for calls, the number of SMS sent, and the amount of data transfer. To avoid excessive billing (a standard telco scam) there should be a requirement that fees for extra use not exceed some small multiple of the base rate, for example if the government was paying $10 for 600 minutes of calls and 1G of data the excess usage charges could be capped at 3 cents per meg and 5 cents per minute (3* the base rate) which would be profitable for the telco but not a scam.

If the telcos act in a market driven competitive manner they will compete to provide the most attractive offerings for $10 per month.

If the build cost of the NBN had been invested at government bond rates (for any of the rates used for current bonds) then it would pay for the mobile phone bills for every resident forever, so the cost of providing phones for everyone is in the range of government telecommunications programs. If people who are working were to pay an extra $10 in tax and people who are on social security had their benefits reduced by $10 then that would be a great deal if it saved them the $20 or more that most people spend on a basic phone plan.

Government Phone Delays

A friend who’s a single mother pays for an “unlimited” mobile phone plan because calls to the social security office are usually kept on hold for more than an hour. It’s likely that she could save money over the course of a year by paying for a cheaper plan and just dealing with the occasional big bill, but she needs to budget carefully and feels that she can’t take that risk. It seems stupid that government phone delays (partly caused by cutting funds for staff) cause increased expenses for people who are receiving social security payments. If the government implemented a smart queuing system that allowed them to call people back instead of making them wait on hold then it would save money overall.

So there are obviously other ways that the government can save money on phone calls and time for everyone.

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Syndicated 2014-05-15 07:53:52 from etbe - Russell Coker

BTRFS vs LVM

For some years LVM (the Linux Logical Volume Manager) has been used in most Linux systems. LVM allows one or more storage devices (either disks, partitions, or RAID sets) to be assigned to a Volume Group (VG) some of which can then allocated to a Logical Volume (LVs) which are equivalent to any other block device, a VG can have many LVs.

One of the significant features of LVM is that you can create snapshots of a LV. One common use is to have multiple snapshots of a LV for online backups and another is to make a snapshot of a filesystem before making a backup to external storage, the snapshot is unchanging so there’s no problem of inconsistencies due to backing up a changing data set. When you create a snapshot it will have the same filesystem label and UUID so you should always mount a LVM device by it’s name (which will be /dev/$VGNAME/$LVNAME).

One of the problems with the ReiserFS filesystem was that there was no way to know whether a block of storage was a data block, a metadata block, or unused. A reiserfsck --rebuild-tree would find any blocks that appeared to be metadata and treat them as such, deleted files would reappear and file contents which matched metadata (such as a file containing an image of a ReiserFS filesystem) would be treated as metadata. One of the impacts of this was that a hostile user could create a file which would create a SUID root program if the sysadmin ran a --rebuild-tree operation.

BTRFS solves the problem of filesystem images by using a filesystem specific UUID in every metadata block. One impact of this is that if you want to duplicate a BTRFS filesystem image and use both copies on the same system you need to regenerate all the checksums of metadata blocks with the new UUID. The way BTRFS works is that filesystems are identified by UUID so having multiple block devices with the same UUID causes the kernel to get confused. Making an LVM snapshot really isn’t a good idea in this situation. It’s possible to change BTRFS kernel code to avoid some of the problems of duplicate block devices and it’s most likely that something will be done about it in future. But it still seems like a bad idea to use LVM with BTRFS.

The most common use of LVM is to divide the storage of a single disk or RAID array for the use of multiple filesystems. Each filesystem can be enlarged (through extending the LV and making the filesystem use the space) and snapshots can be taken. With BTRFS you can use subvolumes for the snapshots and the best use of BTRFS (IMHO) is to give it all the storage that’s available so there is no need to enlarge a filesystem in typical use. BTRFS supports quotas on subvolumes which aren’t really usable yet but in the future will remove the need to create multiple filesystems to control disk space use. An important but less common use of LVM is to migrate a live filesystem to a new disk or RAID array, but this can be done by BTRFS too by adding a new partition or disk to a filesystem and then removing the old one.

It doesn’t seem that LVM offers any benefits when you use BTRFS. When I first experimented with BTRFS I used LVM but I didn’t find any benefit in using LVM and it was only a matter of luck that I didn’t use a snapshot and break things.

Snapshots of BTRFS Filesystems

One reason for creating a snapshot of a filesystem (as opposed to a snapshot of a subvolume) is for making backups of virtual machines without support from inside the virtual machine (EG running an old RHEL5 virtual machine that doesn’t have the BTRFS utilities). Another is for running training on virtual servers where you want to create one copy of the filesystem for each student. To solve both these problems I am currently using files in a BTRFS subvolume. The BTRFS kernel code won’t touch those files unless I create a loop device so I can only create a loop device for one file at a time.

One tip for doing this, don’t use names such as /xenstore/vm1 for the files containing filesystem images, use names such as /xenstore/vm1-root. If you try to create a virtual machine named “vm1″ then Xen will look for a file named “vm1″ in the current directory before looking in /etc/xen and tries to use a filesystem image as a Xen configuration file. It would be nice if there was a path for Xen configuration files that either didn’t include the current directory or included it at the end of the list. Including the current directory in the path is a DOS mistake that should have gone away a long time ago.

Psychology and Block Devices

ZFS has a similar design to BTRFS in many ways and has some similar issues. But one benefit for ZFS is that it manages block devices in a “zpool”, first you create a zpool with the block devices and after that you can create ZFS filesystems or “ZVOL” block devices. I think that most sysadmins would regard a zpool as something similar to LVM (which may or may not be correct depending on how you look at it) and immediately rule out the possibility of running a zpool on LVM.

BTRFS looks like a regular Unix filesystem in many ways, you can have a single block device that you mount with the usual mount command. The fact that BTRFS can support multiple block devices in a RAID configuration isn’t so obvious and the fact that it implements equivalents to most LVM functionality probably isn’t known to most people when they start using it. The most obvious way to start using BTRFS is to use it just like an Ext3/4 filesystem on an LV, and to use LVM snapshots to backup data, this is made even more likely by the fact that there is a program to convert a ext2/3/4 filesystem to BTRFS. This seems likely to cause data loss.

Related posts:

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Syndicated 2014-05-12 07:37:50 from etbe - Russell Coker

Source Escrow for Proprietary Software

British taxpayers are paying for extra support for Windows XP due to a lack of planning by the UK government [1]. While the cost of this is trivial compared to other government stupidity (such as starting wars of aggression) this sort of thing should be stopped.

The best way to solve such problems is for governments to only use free software. If the UK government used Red Hat Enterprise Linux then when Red Hat dropped support for old versions they would have the option of providing their own support for old versions, hiring any other company to support old versions, or paying Red Hat for supporting it. In that case the Red Hat offer would probably be quite reasonable as competition drives the prices down.

It doesn’t seem likely that the UK government will start using only free software in the near future. It’s not impossible to do so, there are organisations dedicated to this task such as Free-gov.org which aims to develop e-government software that is under GPL licenses [2]. The Wikipedia page List of Linux Adopters [3] has a large section on government use, while not all entries are positive (some have reverted) it shows that it’s possible to use Linux for all areas of government. But governments often move slowly and in the case of wealthy countries such as the UK it can be easier to just tax the citizens a little more than to go to the effort of saving money.

But when governments use proprietary software they shouldn’t be restricted in support. It seems that the only way to ensure that the government can do what it needs is to have a source escrow system. Then if the company that owned the software ceased supporting it anyone who wanted to offer support would be able to do so. This would probably require that software which is out of support be released to the public domain so that anyone who wanted to tender for such support work could first inspect the code to determine if they were capable of doing the work.

People who believe the myths about secret source software claim that allowing the source code to be released would damage the company that owns it. This has been proved incorrect by the occasions when source code for software such as MS-Windows has been released on the Internet with no apparent harm. Also Microsoft have a long history of licensing their source code to universities, governments, and other companies for various purposes (including porting Windows to other CPUs). It’s most likely that some part of the UK government already has the full source code to Windows XP, and it’s also quite likely that computer criminals have obtained copies of the source by now for the purpose of exploiting security flaws. Also they stop supporting software when they can’t make money from providing the usual support, so by definition the value to a company of the copyright is approaching zero by the time they decide to cease support.

Given the lack of success experienced by companies that specialise in security (for example the attack on RSA to steal the SecurID data [4]) it doesn’t seem plausible that Microsoft has had much success in keeping the source to Windows XP (or any other widely used product) secret over the course of 12 years.

In summary source code to major proprietary software products is probably available to criminals long before support expires and is of little value to the copyright owners. But access to it can provide value to governments and other users of the software.

The only possible down-side to the software vendor is if the new version doesn’t provide any benefits to the user. This could be a problem for Microsoft who seem to have the users hate every second version of Windows enough to pay extra for the old version. The solution is to just develop quality software that satisfies the needs of the users. Providing a legal incentive for this would be a good idea.

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Syndicated 2014-05-03 05:50:31 from etbe - Russell Coker

Links April 2014

Yves Rossy is the Jetman, he flys with a wing and four jet engines strapped to his body, he gave an interesting TED talk about flying along with some exciting videos [1].

Larry Brilliant gave an informative and inspiring TED talk about stopping pandemics [2]. I thought that Smallpox was the last disease to be eradicated but I was wrong.

Michael Shermer gave an interesting TED talk about pattern recognition and self deception [3]. It’s a pity that the kissing prank shown at the end only pranked women, they should be less sexist and prank men too.

Raffaello D Andrea gave an interesting TED presentation about “Athletic” quadcopters [4]. It’s very impressive and has the potential for several new human/machine sports.

Lisa D wrote an insightful article about Prejudice Spillover discussing the way that people who aren’t in minority groups only seem to care about injustice when a member of the majority is targetted by mistake [5].

Ron Garret wrote an insightful post about the Divine Right of Billionaires which debunks some stupid arguments by a billionaire [6]. Ron says that “it’s often instructive to examine incorrect arguments, especially when those arguments are advanced by smart people” and demonstrates it in this post.

Lisa D wrote an interesting post about her problems with financial aid bureaucracy [7]. She intended the post to be a personal one about her situation, but I think it illustrates problems with the various aid programs. If aid was available to her with less bureaucracy then she would be doing paid work, completing her studies, and heading towards post-graduate studies.

Mark Shuttleworth wrote an insightful article about ACPI, security, and device tree [8]. It’s the first time I’ve seen a good argument for device tree.

TED presented an interesting video-conference interview with Edward Snowden [9]. It’s unusually long by TED standards but definitely worth watching.

Tom Meagher (who’s wife was raped and murdered two years ago) wrote an insightful article about rape culture [10].

Key Lay (the Victorian Chief Commissioner of Police) wrote a good article encouraging men to act to stop violence against women [11]. It’s particularly noteworthy when a senior police officer speaks out about this given the difficulties women have had in reporting such crimes to police.

Emily Baker wrote an insightful article about the lack of support for soldiers who survive war [12]. A lot of attention and money is spent remembering the soldiers who died in the field but little on those who live suffer afterwards, more soldiers die from suicide than enemy fire.

Daniel Pocock wrote an informative article about the failings of SMS authentication for online banking [13]. While he has good points I think he’s a little extreme. Stopping the least competent attackers is still a significant benefit as most potential attackers aren’t that competent.

Jess Zimmerman wrote an interesting article for Time about the “Not All Men” argument that is a current trend in derailing discussions about the treatment of women [14].

The Belle Jar has an insightful article “Why Won’t You Educate Me About Feminism” about some ways that men pretend to care about the treatment of women [15].

Jon Evans wrote an article for Tech Crunch about the “Honywell Bubble Count” measure of diversity in people you follow on social media [16]. Currently on Twitter I follow 57 accounts of which 15 are companies and organisations, so I follow 42 people. I follow 13 women 31%, for a visible minority group other than my own it’s 2/42 or 5%, for people who live in other countries I think it’s 8/42 (although it’s difficult to determine where some people live) which is 19%. So my Honywell number is 55.

The Top Stocks forum has an interesting post by a Coal Seam Gas (CSG) worker [17]. It seems that CSG is even worse than I thought.

Ashe Dryden wrote an informative post for Model View Culture about the backlash that members of minority groups (primarily women) receive when they speak out [18].

Related posts:

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Syndicated 2014-04-30 13:55:26 from etbe - Russell Coker

Autism and the Treatment of Women Again

Background

I’ve previously written about the claim that people use Autism as an excuse for bad behavior [1]. In summary it doesn’t and such claims instead lead to people not being assessed for Autism.

I’ve also previously written about empathy and Autism in the context of discussions about conference sexual harassment [2]. The main point is that anyone who’s going to blame “empathy disorders” for the widespread mistreatment of women in society and divert the subject from the actions of average men to men in minority groups isn’t demonstrating empathy.

Discussions of the actions of average men are so often derailed to cover Autism that the Geek Feminism Wiki has a page about the issue of blaming Autism [3].

The Latest Issue

Last year Shanley Kane wrote an informative article for Medium titled “What Can Men Do” about the treatment of women in the IT industry [4]. It’s a good article, I recommend reading it. As an aside @shanley’s twitter feed is worth reading [5].

In response to Shanley’s article Jeff Atwood wrote an article of the same title this year which covered lots of other things [6]. He writes about Autism but doesn’t seem to realise that officially Asperger Syndrome is now Autism according to DSM-V (they decided that separate diagnosis of Autism, Asperger Syndrome, and PDD-NOS were too difficult and merged them). Asperger Syndrome is now a term that refers to historic issues (IE research that was published before DSM-V) and slang use.

Gender and the Autism Spectrum

Jeff claims that “autism skews heavily towards males at a 4:1 ratio” and cites the Epidemiology of Autism Wikipedia page as a reference. Firstly that page isn’t a great reference, I fixed one major error (which was obviously wrong to anyone who knows anything about Autism and also contradicted the cited reference) in the first section while writing this post.

The Wikipedia page cites a PDF about the Epidemiology of Autism that claims the 4.3:1 ratio of boys to girls [7]. However that PDF is a summary of other articles and the one which originated the 4.3:1 claim is behind a paywall. One thing that is worth noting in the PDF is that the section containing the 4.3:1 claim also references claims about correlations between race and Autism and studies contradicting such claims – it notes the possibility of “ascertainment bias”. I think that anyone who reads that section should immediately consider the possibility of ascertainment bias in regard to the gender ratio.

Most people who are diagnosed with Autism are diagnosed as children. An Autism diagnosis of a child is quite subjective, an important part is an IQ test (where the psychologist interprets the intent of the child in the many cases where answers aren’t clear) to compare social skills with IQ. So whether a child is diagnosed is determined by the psychologist’s impression of the child’s IQ vs the impression of their social skills.

Whether a child is even taken for assessment depends on whether they act in a way that’s considered to be obviously different. Any child who is suspected of being on the Autism Spectrum will be compared other children who have been diagnosed (IE mostly boys) and this will probably increase the probability that a boy will be assessed. So an Aspie girl might not be assessed because she acts like other Aspie girls not like the Aspie boys her parents and teachers have seen.

The way kids act is not solely determined by neuro-type. Our society expects and encourages boys to be louder than girls and take longer and more frequent turns to speak, this is so widespread that I don’t think it’s possible for parents to avoid it if their kids are exposed to the outside world. Because of this boys who would be diagnosed with Asperger Syndrome by DSM-IV tend to act in ways that are obviously different from other kids. While the combination of Autism and the the social expectations on girls tends to result in girls who are quiet, shy, and apologetic. The fact that girls are less obviously different and that their differences cause fewer difficulties for parents and teachers makes them less likely to be assessed. Note that the differences in behavior of boys and girls who have been diagnosed is noted by the professionals (and was discussed at a conference on AsperGirls that my wife attended) while the idea that this affects assessment rates is my theory.

Jeff also cites the book “The Essential Difference: Male And Female Brains And The Truth About Autism” by Professor Simon Baron-Cohen (who’s (in)famous for his “Extreme Male Brain” theory). The first thing to note about the “Extreme Male Brain” theory are that it depends almost entirely on the 4.3:1 ratio of males to females on the Autism Spectrum (which is dubious as I noted above). The only other evidence in support of it is subjective studies of children which suffer from the same cultural issues – this is why “double blind” tests should be used whenever possible. The book Delusions of Gender by Cordelia Fine [8] debunks Simon Baron-Cohen’s work among other things. The “look inside” feature of the Amazon page for Delusions of Gender allows you to read about Simon Baron-Cohen’s work [9].

Now even if the “Extreme Male Brain” theory had any merit it would be a really bad idea to cite it (or a book based on it) if you want to make things better for women in the IT industry. Cordelia’s book debunks the science and also shows how such claims about supposed essential difference are taken as exclusionary.

The Problem with Jeff Atwood

Jeff suggests in his post that men should listen to women. Then he and his followers have a huge flame-war with many women over twitter during which which he tweeted “Trying to diversify my follows by following any female voices that engaged me in a civil, constructive way recently“. If you only listen to women who agree with you then that doesn’t really count as listening to women. When you have a stated policy of only listening to women who agree then it seems to be more about limiting what women may feel free to say around you. The Geek Feminism wiki page about the “Tone Argument [10] says the following:

One way in which the tone argument frequently manifests itself is as a call for civility. A way to gauge whether a request for civility is sincere or not is to ask whether the person asking for civility has more power along whatever axes are contextually relevant (see Intersectionality) than the person being called “incivil”, less power, or equal power. Often, people who have the privilege of being listened to and taken seriously level accusations of “incivility” as a silencing tactic, and label as “incivil” any speech or behavior that questions their privilege. For example, some men label any feminist thought or speech as hostile or impolite; there is no way for anybody to question male power or privilege without being called rude or aggressive. Likewise, some white people label any critical discussion of race, particularly when initiated by people of color, as incivil.

Writing about one topic is also a really good idea. A blog post titled “What Can Men Do” should be about things that men can do. Not about Autism, speculation about supposed inherent differences between men and women which are based on bad research, gender diversity in various occupations, etc. Following up a post on “What Can Men Do” with discussion (in blog comments and twitter) about what women should do before they are allowed to join the conversation is ridiculous. Jeff’s blog post says that men should listen to women, excluding women based on the tone argument is gross hypocrisy.

Swearing

Jeff makes a big deal of the fact that Shanley uses some profane language in her tweets. This combines a couple of different ways of silencing women. It’s quite common for women to be held to a high standard of “ladylike” behavior, while men get a free pass on doing the same thing. One example of this is the Geek Feminism article about the results of Sarah Sharp’s request for civility in the Linux kernel community [11]. That’s not an isolated incident, to the best of my recollection in 20+ years my local Linux Users Group has had only one debate about profanity on mailing lists – in that case a woman (who is no longer active in the group) was criticised for using lesser profanity than men used both before and after with no comment (as an experiment I used some gratuitous profanity a couple of weeks later and no-one commented).

There is also a common difference in interpretation of expressions of emotion, when a woman seems angry then she invariably has men tell her to change her approach (even when there are obvious reasons for her anger) while when a man is angry the possibility that other people shouldn’t make him angry will usually be considered.

The issues related to the treatment of women have had a large affect on Shanley’s life and her friend’s lives. It’s quite understandable that she is angry about this. Her use of profanity in tweets seems appropriate to the situation.

Other Links

Newsweek’s “Gentlemen” in Technology article has a section about Jeff [12], it’s interesting to note his history of deleting tweets and editing his post. I presume he will change his post in response to mine and not make any note of the differences.

Jacob Kaplan-Moss wrote a good rebuttal to Jeff’s post [13]. It’s a good article and has some other relevant links that are worth reading.

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Syndicated 2014-04-29 05:43:36 from etbe - Russell Coker

Swap Breaking SSD

I’ve seen many comments about swap space and SSD claiming that swap will inherently destroy SSD through using too many writes. The latest was in the comments of my post about swap space and SSD performance [1]. Note that I’m not criticising the person who commented on my blog, everyone has heard lots of reports about possible problems that they avoid without analysing them in detail.

The first thing to note is that the quality of flash memory varies a lot, the chips that are used in SSDs for workstation/server use are designed to last while those in USB-flash devices aren’t. I’ve documented my unsuccessful experiments with using USB-flash for the root filesystem of a gateway server [2] (and the flash device that wasn’t used for swap died too).

The real issue when determining whether swap will break your SSD is the amount of writes. While swapping can do a lot of writing quickly that usually doesn’t happen unless something has gone wrong. The workstation that I’m currently using has writes to the root fileystem outnumbering writes to swap by a factor of 130:1 (by volume of data written). On other days I’ve seen it as low as 42:1, in either case it’s writes to the root filesystem (which is BTRFS and includes /home etc) that will break the SSD if anything. For some other workstations I run I see ratios of 201:1 (that’s with 8G of RAM), 57:1, and 23:1. In a quick search I couldn’t find a single system I run where even 10% of disk writes were attributed to swap. This really isn’t surprising given that adding RAM is a cheap way to improve the performance of most systems. If a SSD didn’t do any write leveling (as is rumored to be the case with cheap USB flash devices) then swap use might still cause a problem because of the number of writes in a small area, but if that was the case then filesystem journals and other fixed data structures would be more likely to cause a problem – and any swap based breakage would break swap not the root filesystem (although if swap was the first partition then it might also break the MBR).

Of the workstations that are convenient to inspect the one with the most writes to the root filesystem and swap space (IE everything on /dev/sda) had 128G written per day for 1.2 days of uptime, but that involved running a filesystem balance and some torrent downloads (not the typical use). Among the two systems which had been running for more than 48 hours with typical use the most writes was 24G in a day. If a SSD can sustain 10,000 writes per block (which is smaller than quoted by most flash manufacturers nowadays) and has perfect wear leveling (which is unlikely) then the system with a 120G SSD and 128G written in a day could continue like that for almost 10,000 days or 27 years – much longer than storage is expected to work or be useful. So for workstation use (where even 24G of writes per day probably counts as heavy use) a 120G SSD that can sustain 10,000 writes per block shouldn’t be at great risk of wearing out.

Conclusion

I believe that swap is much less likely to break SSDs than regular file access on every system with a reasonable amount of RAM. For systems which don’t have enough RAM you probably want the speed of SSD for swap space anyway in spite of the risks.

If wear leveling works as designed and the 10,000+ writes per block claims are accurate then SSDs will massively outlast their useful life. Long before they wear out they should be too small, too slow, and probably not compatible. 26 years ago I had a 5.25″ full height ST-506 disk in my desktop PC, it wouldn’t physically fit in most systems I own now (unless I removed the DVD drive), there is no possibility of buying a controller (I don’t own a system with an ISA bus), and that disk was too slow and small by today’s standards. A 27yo SSD isn’t going to be useful for anything, even for archive storage it’s no good as no-one has tested long term storage and data could decay before then.

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Syndicated 2014-04-27 02:30:04 from etbe - Russell Coker

BTRFS Status April 2014

Since my blog post about BTRFS in March [1] not much has changed for me. Until yesterday I was using 2.13 kernels on all my systems and dealing with the occasional kmail index file corruption problem.

Yesterday my main workstation ran out of disk space and went read-only. I started a BTRFS balance which didn’t seem to be doing any good because most of the space was actually in use so I deleted a bunch of snapshots. Then my X session aborted (some problem with KDE or the X server – I’ll never know as logs couldn’t be written to disk). I rebooted the system and had kernel threads go into infinite loops with repeated messages about a lack of response for 22 seconds (I should have photographed the screen). When it got into that state the ALT-Fn keys to change a virtual console sometimes worked but nothing else worked – the terminal usually didn’t respond to input.

To try and stop the kernel from entering an infinite loop on every boot that I used “rootflags=skip_balance” on the kernel command line to stop it from continuing the balance which made the system usable for a little longer, unfortunately the skip_balance mount option doesn’t permanently apply, the kernel will keep trying to balance the filesystem on every mount until a “btrfs balance cancel” operation succeeds. But my attempts to cancel the balance always failed.

When I booted my system with skip_balance it would sometimes free some space from the deleted snapshots, after two good runs I got to 17G free. But after that every time I rebooted it would report another Gig or two free (according to “btrfs filesystem df“) and then hang without committing the changes to disk.

I solved this problem by upgrading my USB rescue image to kernel 3.14 from Debian/Experimental and mounting the filesystem from the rescue image. After letting kernel 3.14 work on the filesystem for a while it was in a stage where I could use it with kernel 3.13 and then boot the system normally to upgrade it to kernel 3.14.

I had a minor extra complication due to the fact that I was running “apt-get dist-upgrade” at the time the filesystem went read-only do the dpkg records of which packages were installed were a bit messed up. But that was easy to fix by running a diff against /var/lib/dpkg/info on a recent snapshot. In retrospect I should have copied from an old snapshot of the root filesystem, but I fixed the problems faster than I could think of better ways to fix them.

When running a balance the system had a peak IO rate of about 30MB/s reads and 30MB/s writes. That compares to the maximum contiguous file IO speed of 260MB/s for reads and 320MB/s for writes. During that time it had about 50% CPU time used for my Q8400 quad-core CPU. So far the only tasks that I do regularly which have CPU speed as a significant bottleneck are BTRFS filesystem balancing and recoding MP4 files. Compiling hasn’t been an issue because recently I haven’t been compiling many programs that are particularly big.

Lessons Learned

I should photograph the screen regularly when doing things that won’t be logged, those kernel error messages might have been useful to me or someone else.

The fact that the only kernel that runs BTRFS the way I need comes from the Experimental repository in Debian stands in contrast to the recent kernel patch that stops describing BTRFS as experimental. While I have a high opinion of the people who provide support for the kernel in commercial distributions and their ability to back-port fixes from newer kernels I’m concerned about their decision to support BTRFS. I’m also dubious about whether we can offer BTRFS support in Debian/Jessie (the next version of Debian) without a significant warning. OTOH if you find yourself with a BTRFS system that isn’t working well you could always hire me to fix it. I accept payment via Paypal, bank transfer, or Bitcoin. If you want to pay me in Grange then I assure you I will never forget about it. ;)

I thought that I wouldn’t have CPU speed issues when I started using the AMD64 architecture, for most tasks that’s been the case. But for systems for which storage is important I’ll look at getting faster CPUs because of BTRFS. Using faster CPUs for storage isn’t that uncommon (I used to work for SGI and dealt with some significant CPU power used for file serving), but needing a fast quad-core CPU to drive a single SSD is a little disappointing. While recovery from file system corner cases isn’t going to be particularly common it’s something that you want completed quickly, for personal systems you want to be doing something else and for work systems you don’t want down-time.

The BTRFS problems with running out of disk space are really serious. It seems that even workstations used at home can’t survive without monitoring. For any other filesystem used at home you can just let it get full and then delete stuff.

Include “rootflags=skip_balance” in the boot loader configuration for every system with a BTRFS root filesystem and in the /etc/fstab for every non-root BTRFS filesystem. I haven’t yet encountered a single situation where continuing the balance did any good or when it didn’t do any harm.

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Syndicated 2014-04-26 09:31:30 from etbe - Russell Coker

Sociological Images 2014

White Trash

The above poster was on a bridge pylon in Flinders St in 2012. It’s interesting to see what the Fringe Festival people consider to be associated with “white trash”. They claim homophobia is a “white trash” thing however lower class people have little political power and the fact that we still don’t have marriage equality in Australia is clear evidence that homophobia is prevalent among powerful people.

Toys vs Fairies

Fairies look pretty while boys toys do things

I took the above photo at Costco in 2012. I think it’s worth noting the way that the Disney Fairies (all female and marketed to a female audience) are standing around looking pretty while the Toy Story characters (mostly male and marketed to a male audience) are running out to do things. Having those items side by side on the shelf was a clear example of a trend in toys towards girls being encouraged to be passive while boys are doing things. The Toy Story pack has one female character, so it could be interpreted as being aimed at both boys and girls. But even that interpretation doesn’t remove the clear gender difference.

It seems ironic to me that the descriptions on the boxes are “Read, Play, and Listen” for the Toy Story pack and “Read, Play, and Colour” on the Fairies pack. Colouring is more active than listening so the pictures don’t match the contents.

Make Up vs Tools

Girls chocolate is make-up and boys chocolate is tools

I took the above photo in an Aldi store in early 2013, today I was in Aldi and noticed that the same chocolate is still on sale. A clear and pointless gender difference. Rumor has it that some of the gender difference in kids clothing is so that a child can’t wear the clothes of an older sibling of different gender, but chocolate only gets eaten once so there is no reason for this.

Oath

The above poster was inside the male toilet at Melbourne University in 2013. It would probably be good to have something like that on display all the time instead of just for one event.

Locks

Locks with inscriptions on a bridge on the Yarra River in Melbourne

I took the above picture early this year, it shows hundreds of padlocks attached to a bridge across the Yarra River in Melbourne. Each padlock has a message written or inscribed in it, mostly declarations of love. I first noticed this last year, I’m not sure how long it’s been up. There was nothing formal about this (no signs about it), people just see it and decide that they want to add to it. I guess that the council cuts some of them off periodically as the number of locks doesn’t seem to be increasing much in recent times.

It would be interesting to do some research into how many locks are needed to start one of these. It would also be interesting to discover whether the nature of the inscriptions determines the speed at which it takes off, would a bunch of padlocks with messages like “I Love Linux” inspire others as well as messages declaring love for random people? All that is required is some old locks and an engraving tool.

I wonder what the social norm might be regarding messing with those locks. If I was to use those padlocks to practice the sport of lock-picking (which I learned when in Amsterdam) I wonder whether random bystanders would try to discourage me. It seems likely that picking the locks and taking them away would get a negative reaction but I wonder whether picking them one at a time and replacing them (or maybe moving them to another wire) would get a reaction.

Blackface for Schoolkids

teachers choice blackface and yellowface masks

A craft shop at the Highpoint shopping center in Melbourne is selling “Teacher’s Choice” brand “Multicultural Face Masks”. “Multicultural” is a well regarded term in education, teaching children about other cultures is a good concept but can be implemented really badly. When I was in high school the subject “Social Studies” seemed to have an approach of “look how weird people are in other places” instead of teaching the kids anything useful.

Sociological Images has an informative article on the Australian Hey Hey it’s Saturday blackface incident in 2009 [1].

The idea of these masks seems to involve students dressing up as caricatures of other races. The mask which looks like someone’s idea of a Geisha is an even bigger WTF, mixing what the package calls “culture” (really race) with sex work. When I visited Tokyo I got the impression that “French maids” fill a similar niche to Geisha for younger Japanese men and the “maid cafe” thing is really popular there. I think it’s interesting to consider the way that a French maid costume is regarded differently to a Geisha costume. I expect that “Teacher’s Choice” doesn’t sell French maid costumes.

Delicious Cow

picture of a bovine named Delicious

Usually meat is advertised in a way that minimises the connection to living animals. Often adverts just show cuts of meat and don’t make any mention of animals and when animals are shown they are in the distance. The above picture was on the wall at a Grill’d burger restaurant in Point Cook. It shows a bovine (looks like a bull even though I believe that cows are the ones that are usually eaten) with a name-tag identifying it as “Delicious”. The name tag personalises the animal which is an uncommon thing to do when parts of an animal are going to be eaten.

Of the animals that are commonly eaten it seems that the general trend is to only show fish as complete live animals, presumably because people can identify with mammals such as cattle in a way that they can’t identify with fish. Fish are also the only complete animals that are shown dead, adverts for fish that are sold as parts (EG salmon and tuna) often show complete dead fish. But I’ve never seen a meat advert that shows a complete dead cow or sheep.

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Syndicated 2014-04-21 02:00:23 from etbe - Russell Coker

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