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Date: Fri, 10 Aug 2012 12:28:02 +0200
From: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
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Subject: Re: [Qemu-devel] virtio-scsi vs. virtio-blk
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>

I'm using iscsi. So no raw or qcow2. XFS as FS.

Thanks,

Stefan

Am 10.08.2012 12:20, schrieb Paolo Bonzini:
> Il 10/08/2012 11:22, Stefan Priebe - Profihost AG ha scritto:
>> virtio-scsi is now working fine. Could you please help me to get discard
>> / trim running? I can't find any information what is needed to get
>> discard / trim working.
>
> You need to add discard_granularity=NNN, where NNN is usually 512 for
> raw and the cluster size (65536) for qcow2.
>
> However, discard is supported only for XFS on raw, and on qcow2 it will
> not reclaim space---the space will only be reused for future qcow2
> allocation.
>
> Better support for discard on raw (other filesystems + block devices),
> and more efficient support also on other formats is on my todo list for
> the future.  However, an efficient implementation unfortunately requires
> changes at all levels including the kernel.
>
> I hope to present something about it at KVM Forum.
>
> Paolo
>