[dm-crypt] poor mysqldump performance

Tracy Reed treed at ultraviolet.org
Fri Feb 24 03:55:10 CET 2012

On Fri, Feb 24, 2012 at 01:29:54AM +0000, Alasdair G Kergon spake thusly:
> Have you done much tuning, in particular /sys/block/<devices>/queue/nr_requests ?
> http://www.redbooks.ibm.com/redpapers/pdfs/redp4285.pdf remains a good background
> read.

Given that a non-dmcrypt mysqldump on the same disks (different logical volume)
finishes and 15 minutes and a dmcrypt mysql backup happens in 30 minutes any
tuning being done would have to be dmcrypt-specific and affect something in the
dmcrypt layer or above, correct?

nr_requests only exists for the physical disk device. Just for kicks I just
bumped it up to 8192 from the default 1024 and ran my test again. Same
performance: Twice as slow as without dmcrypt.

Tracy Reed

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