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

[Brian Candler]

On Thu, Jul 12, 2012 at 12:04:24PM +0300, Samuli Heinonen wrote:
> >So am I kidding myself that approaching 45-50MB/s with a
> >FUSE based Gluster mount and using cache=writethrough is actually
> >a safe thing to do really?
...
> When using writethrough the data is written to cache but not marked
> finished before it has hit the disk. Data in cache can be then used
> to speed up read operations. So I would consider it pretty safe, but
> perhaps someone else can explain it better?

I don't believe he is getting that speed with cache=writethrough.  I think
he means cache=writeback.

http://www.linux-kvm.org/page/Tuning_KVM
"QEMU also supports a wide variety of caching modes. Writeback is useful for
testing but does not offer storage guarantees. Writethrough (the default) is
safer, and relies on the host cache."