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Re: [Qemu-devel] [PATCH] Default to cache=writeback
From: |
Alexander Graf |
Subject: |
Re: [Qemu-devel] [PATCH] Default to cache=writeback |
Date: |
Tue, 1 Jun 2010 13:31:32 +0200 |
On 26.05.2010, at 21:28, Stefan Hajnoczi wrote:
> On Wed, May 26, 2010 at 7:13 PM, Alexander Graf <address@hidden> wrote:
>> In the previous discussion Anthony brought up the fact that cache=writeback
>> is
>> safe enough considering data integrity. If so, I don't see a reason not to
>> use
>> it as default, as it speeds up things a lot.
>
> cache=writeback is not a good default for qcow2:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=572825
> http://wiki.qemu.org/Features/Qcow2DataIntegrity
>
> The actual qcow2 file itself can become corrupted because metadata
> updates are not ordered or flushed with respect to each other or data.
> This is more serious than losing data written after the last flush.
>
> I believe special case cache= defaults for raw vs qcow2 have been
> mentioned before but I don't see any code in qemu.git currently that
> ensures qcow2 is run safely by default.
Well since cache=writethrough is the default, it apparently isn't hit by the
issues you mentioned.
Kevin, what's your opinion on this?
Alex
- Re: [Qemu-devel] [PATCH] Default to cache=writeback,
Alexander Graf <=