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Date: Fri, 04 Oct 2013 14:45:58 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] Using TRIM to shrink qcow2 images
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To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: QEMU Developers <qemu-devel@nongnu.org>

Il 04/10/2013 09:07, Alexey Kardashevskiy ha scritto:
> On 10/04/2013 05:05 PM, Paolo Bonzini wrote:
>> Il 04/10/2013 08:22, Alexey Kardashevskiy ha scritto:
>>>
>>> btw I tried "discard=on" as you described (with if=virtio) and received
>>> an error:
>>> [root@localhost ~]# fstrim -v /
>>> fstrim: /: FITRIM ioctl failed: Operation not supported
>>>
>>> In my case if=virtio means virtio-blk. If I use virtio-scsi or ibmvscsi,
>>> fstrim works just fine but failing virtio-blk bothers me a bit as we
>>> might have a bug in ppc64, do not we? (we == ppc64 folks, of course :) )
>>>
>>
>> No, virtio-blk does not support trim.
> 
> So the example was broken or if=virtio uses virtio-scsi (instead of
> virtio-blk) on x86?

It was broken.  IDE works, as well as any SCSI HBA (including USB storage).

Paolo