Re: Shouldn't cache=none be the default for drives?

[Thomas Mueller <thomas@chaschperli.ch>]

Am Wed, 07 Apr 2010 16:39:41 +0200 schrieb Troels Arvin:

> Hello,
> 
> I'm conducting some performancetests with KVM-virtualized CentOSes. One
> thing I noticed is that guest I/O performance seems to be significantly
> better for virtio-based block devices ("drive"s) if the cache=none
> argument is used. (This was with a rather powerful storage system
> backend which is hard to saturate.)
> 
> So: Why isn't cache=none be the default for drives?

while ago i suffered poor performance of virtio and win2008. 

This helped alot:

I enabled "deadline" block scheduler instead of the default "cfq" on the 
host system. tested with: Host Debian with scheduler deadline, Guest 
Win2008 with Virtio and cache=none. (26MB/s to 50MB/s boost measured) 
Maybe this is also true for Linux/Linux.

I expect that scheduler "noop" for linux guests would be good.

- Thomas