21 Dec 2009 dkg   » (Master)

dd, netcat, and disk throughput

I was trying to dump a large Logical Volume (LV) over ethernet from one machine to another. I found some behavior which surprised me.

fun constraints

  • I have only a fairly minimal debian installation on each machine (which fortunately includes netcat-traditional)
  • The two machines are connected directly by a single (gigabit) ethernet cable, with no other network connection. So no pulling in extra packages.
  • I have serial console access to both machines, but no physical access.
  • The LV being transfered is 973GB in size according to lvs (fairly large, that is), and contains a LUKS volume, which itself contains a basically-full filesystem -- transferring just the "used" bytes is not going to save space/time.
  • I want to be able to check on how the transfer is doing while it's happening.
  • I want the LV to show up as an LV on the target system, and don't have tons of extra room on the target to play around with (so no dumping it to the filesystem as a disk image first).

(how do i get myself into these messes?)

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Syndicated 2009-12-21 06:21:00 from Weblogs for dkg

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