[ovirt-users] How do I get discard working?

[Amador Pahim]

On 06/10/2015 03:24 PM, Fabian Deutsch wrote:
> ----- Original Message -----
>> oVirt Node - 3.5 - 0.999.201504280931.el7.centos
>>
>> Using our shared storage via baremetal (stock CentOS 7) -> iscsi, I can
>> successfully issue fstrim commands. With oVirt at the VM level, even
>> with direct LUNS, trim commands are not supported despite having the LVM
>> config in the VMs set up to allow it.
> Hey,
>
> IIUIC you try to get discard working for VMs? That means that if fstrim is
> used inside the VM, that it is getting passed down?
>
> The command line needed for qemu to support discards is:
>
> $ qemu … -drive if=virtio,cache=unsafe,discard,file=<disk> …
>
> I'm not sure which qemu disk drivers/busses support this, but at least virtio does so.
> I'm using it for development.
>
> You could try a vdsm hook to modify the qemu command which is called when the VM is spawned.
>
> Let me know if you can come up with a hook to realize this!

There's this hook in code review intended  to do so:
https://gerrit.ovirt.org/#/c/29770/

>
> Greetings
> fabian
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