[virt-tools-list] Default use of caching on raw volumes
Jamin W. Collins
jcollins at asgardsrealm.net
Wed Aug 18 15:18:37 UTC 2010
On 08/18/2010 09:06 AM, Daniel P. Berrange wrote:
> It is not as clearcut as you make it out to be. If cache=none was always
> the best option,
Show me a single test case using raw volumes where it's not. Every test
I've done and those of others documented online indicate that disabling
caching provides a better performance. Qemu's own website indicates
it'll provide a better performance.
> then QEMU/KVM would have that as their defaults. If there
> is a reason for QEMU not to have this as the default, this applies equally
> to libvirt, hence why libvirt does not override the default for this.
This is a little more than a straw man (if at all). QEMU/KVM provide
little in the way of sensible defaults. Upper level tools provide saner
defaults all the time. For example the guest VM templates used by
virt-manager to default to different NIC or HD emulation or virtio. The
upper level tools provide alternate defaults that tend to provide a
better end user experience through better performance.
> The default should be chosen at either the base layer implementing
> the feature, or by the apps using the feature. libvirt is simply an
> API for accessing the features, not a place to enforce policy
See above. Is this not the list for virt-manager as well? Isn't
virt-manager already providing per guest defaults that differ from the
Why insist on providing a sub-optimal end user experience? Especially
when the necessary change is known and relatively simple.
Jamin W. Collins
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