[Gluster-users] Gluster v 3.3 with KVM and High Availability

[Brian Candler]

On Wed, Jul 11, 2012 at 11:20:16AM -0500, Mark Nipper wrote:
> 	Just as a sanity check for our own setup, write
> performance out of the box with KVM (managed via libvirt) is
> awful, like less than 5MB/s because the disk cache mode is set to
> none by default.

Same as what I see.

> 	But changing this to writeback or writethrough is still
> considered acceptable and safe, correct?

cache=writethrough is the default (slow) mode, and is safe.

cache=writeback is is positively unsafe, and only acceptable if you don't
care about possible data loss.

http://www.linux-kvm.org/wiki/images/5/59/Kvm-forum-2011-performance-improvements-optimizations-D.pdf
"Cache=writeback - Not supported"

> But my understanding from reading previous posts on this
> list is that using something other than a cache mode of none is
> acceptable and safe with Gluster at least.

cache=none is definitely what we want, but doesn't currently work with
glusterfs.

Regards,

Brian.