[libvirt-users] fstrim support in libvirt/qemu guests

[Brian Rak]

On 11/3/2014 8:43 AM, Andrey Korolyov wrote:
> On Mon, Nov 3, 2014 at 4:24 PM, Michal Privoznik <mprivozn at redhat.com> wrote:
>> On 01.11.2014 05:30, Dennis Jacobfeuerborn wrote:
>>> Hi,
>>> I'm trying to find out how to enable fstrim support for libvirt/qemu
>>> guests. Specifically I'm trying to enable this on a CentOS 7 host (qemu
>>> 1.5). I searched the web but only found very vague information and no
>>> clear documentation on the requirements or how to modify the guest xml
>>> to enable discard/fstrim support.
>>>
>>> Can someone point me in the right direction?
>>
>> One thing that you'll need is the guest agent:
>>
>>    http://wiki.libvirt.org/page/Qemu_guest_agent
>>
>> Then you can just use:
>>
>>    # virsh domfstrim $dom
>>
>> Michal
> ... and probably discard-aware block driver (although I cannot name
> anything except virtio-blk which is not supporting trim or will not
> support in the near future). Not sure to which part, guest-host
> interaction or driver abilities, the initial question belongs.
>
>

The virtio-scsi driver supports it, though you take a minor performance 
hit for switching.