Ubuntu
lvm2 package

  1. Bug #129488
  2. Comment #0

Comment 0 for bug 129488

Revision history for this message
James Troup (elmo) wrote : insane default readahead settings on device and unused readahead setting in LVM

Binary package hint: lvm2

When you create an LV, the device ends up with a readahead of 256 bytes. A normal (non-LVM) device's readahead appears to default to 8192 bytes. This makes LVM FSs benchmark (and perform) very badly (our read rate dropped from 320M/s to 90M/s).

To make matters worse, LVM has an internal 'read ahead sectors' variable which is apparently unused, but still displayed by e.g. lvdisplay which just adds to the confusion.

This is apparently a known issue upstream, but not considered a priority:

http://linux.msede.com/lvm_mlist/archive/2004/06/0108.html