From: Kevin Wolf <kwolf@redhat.com>
To: Ivan Ren <renyime@gmail.com>
Cc: mreitz@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v3] qcow2: fix preallocation with metadata on bare block device
Date: Fri, 11 May 2018 19:29:01 +0200 [thread overview]
Message-ID: <20180511172901.GC5016@localhost.localdomain> (raw)
In-Reply-To: <1526053004-12268-1-git-send-email-ivanren@tencent.com>
Am 11.05.2018 um 17:36 hat Ivan Ren geschrieben:
> Create a qcow2 directly on bare block device with
> "-o preallocation=metadata" option. When read this qcow2, it will
> return pre-existing data on block device. This patch add
> QCOW_OFLAG_ZERO flag (supported in qcow_version >= 3) for
> preallocated l2 entry to avoid this problem.
>
> Signed-off-by: Ivan Ren <ivanren@tencent.com>
Doesn't this defeat the purpose of preallocation? Usually, the idea with
preallocation is that you don't need to update any metadata on the first
write, but if you set QCOW_OFLAG_ZERO, we do need a metadata update
again.
So what's the advantage compared to not preallocating at all?
Kevin
next prev parent reply other threads:[~2018-05-11 17:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-11 15:36 [Qemu-devel] [PATCH v3] qcow2: fix preallocation with metadata on bare block device Ivan Ren
2018-05-11 17:29 ` Kevin Wolf [this message]
2018-05-13 13:37 ` Ivan Ren
2018-05-14 6:23 ` Kevin Wolf
2018-05-14 14:30 ` Ivan Ren
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