Am running WordPress importers; that which required more than 30 minutes to import – utilising less than 2% CPU for the whole time – suddenly required less than 3 minutes after adding the
nobarrier option to the root mountpoint and rebooting.
barrier=<0|1(*)> barrier(*) nobarrier
This enables/disables the use of write barriers in the jbd code. barrier=0 disables, barrier=1 enables. This also requires an IO stack which can support barriers, and if jbd gets an error on a barrier write, it will disable again with a warning. Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance penalty. If your disks are battery-backed in one way or another, disabling barriers may safely improve performance. The mount options “barrier” and “nobarrier” can also be used to enable or disable barriers, for consistency with other ext4 mount options.
Gah. Hasn’t Linux gotten past this fuckwittage yet? #ZFS