On Wed, Jun 29, 2011 at 06:17:02PM +0400, Michael Tokarev wrote: > > Honestly, I don't know. Usually the problem is resolved with setting a > > different cache option, so nobody bothers to ask for details. I'd guess > > that it's ext4 in most cases. > > Extremly poor performance also happens on raw devices -- > be it lvm volumes or plain partitions, so that's w/o > any filesystem.
Depends on your setup. If you have ATA devices that have WCE=1 it will suck due to the non-queueable FLUSH command. If you have an older kernel with the draining barriers semantics it will to. If you run on a SAS disk or FC array with WCE=0 performance will be quite good and close to native performance on these. That's all assuming you use O_DIRECT. using cache=writhrough as-is will suck everywher.
