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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off (O_DIRECT) |
Date: | Tue, 20 May 2008 19:58:34 -0500 |
User-agent: | Thunderbird 2.0.0.14 (X11/20080501) |
Paul Brook wrote:
When sector-aligned guest offsets are converted to sector-unaligned writes (e.g. due to qcow2 etc.), that property is no longer satisfied, and power failure of the host disk can cause more damage than the guest is designed to be resistant to.Seems like the easiest solution would be to have qcow always align its writes.We don't do on the fly compression, so it should be fairly easy to make this happen with minimal overhead.
That's not sufficient. O_DIRECT imposes not only offset alignment requirements but also requirements on the buffer being read to. Most of the code in QEMU does not properly align the read/write buffers.
Regards, Anthony Liguori
Paul
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