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Re: Migration with ``drive-mirror`` + NBD will let quorum qcow2 image be
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From: |
Kevin Wolf |
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Subject: |
Re: Migration with ``drive-mirror`` + NBD will let quorum qcow2 image become larger |
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Date: |
Tue, 19 May 2020 11:15:44 +0200 |
Am 19.05.2020 um 10:32 hat Tao Xu geschrieben:
> Hi,
>
> I am using ``drive-mirror`` + NBD for live storage migration. But I find
> that if I use a qcow2 image(virtual size: 10 GiB, disk size: 1.8 GiB) as a
> child of quorum, then the destination image become larger(virtual size: 10
> GiB, disk size: 10 GiB). However if I use a qcow2 image directly, then the
> destination image(virtual size: 10 GiB, disk size: 1.8 GiB) will be equal to
> the source.
>
> So I am wondering if my usage is wrong or it is expected with
> quorum+drive-mirror?
This seems to be because the quorum block driver doesn't implement the
.bdrv_co_block_status interface, so the mirror block job can't know that
some blocks are unallocated/zeroed, but will copy everything.
I'm not sure if quorum can even implement this interface because the
allocation status in different quorum children may differ and voting
might not make sense. But maybe it could return a limited set of flags
at least so that the mirror job can get the BDRV_BLOCK_ZERO information
if the quorum children agree on it.
tl;dr: With quorum + drive-mirror it is currently expected.
Kevin