[fedora-virt] Virt Disk Performance

[Kevin Wolf]

Am 30.10.2011 21:59, schrieb Richard W.M. Jones:
>> I've pulled most of the information you requested. See above. I
>> don't see any specific cache settings on either machine. Is there
>> somewhere I would see the default setting on the machine?
> 
> I'm out of the loop on what the default caching policy is these days.
> Hopefully libvirt is at least choosing a safe one.

cache=writethrough is the default. And indeed this is the safest option,
and at the same time by far the slowest option. I would expect that you
get much better write performance with cache=none.

Note however that older guests OSes cannot deal correctly with disks
that have a volatile write cache, like cache=none emulates. This means
that in case of a host crash and with some bad luck, your guest might
experience file system corruption.

Recent guest OSes are safe in this respect and can be used with
cache=none or cache=writeback in order to improve performance without
any such risk.

Kevin