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Re: [Qemu-devel] Default cache mode
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] Default cache mode |
Date: |
Wed, 29 Jun 2011 16:21:42 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 |
Am 29.06.2011 16:12, schrieb Christoph Hellwig:
> On Wed, Jun 29, 2011 at 04:11:53PM +0200, Kevin Wolf wrote:
>> If the guest is acting correctly, then this assumption is definitely
>> true with cache=none/writeback. What needs to happen is that the guest
>> issues a disk flush before sending your "transaction ok" message. If it
>> doesn't do that it can fail even on real hardware. cache=writethrough
>> makes things safe that aren't even safe on real hardware, that's why I
>> consider it extremely conservative.
>
> Depends on your defintion of real hardware. Traditionally disks always
> had WCE=0 semantics. When ATA disks added volatile writecaches and people
> started seeing problems due to it the advertisement of cache modes and
> cache flush commands were added. For non-ATA disks like SAS or FC
> WCE=1 still is the typical delivery setting.
Sure, I'm not saying that it definitely breaks on any hardware, just
that it can break.
Kevin
- Re: [Qemu-devel] Default cache mode, (continued)
- Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Anthony Liguori, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Stefan Hajnoczi, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Frediano Ziglio, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Kevin Wolf, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29
- Re: [Qemu-devel] Default cache mode,
Kevin Wolf <=
Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29
Re: [Qemu-devel] Default cache mode, Anthony Liguori, 2011/06/29
Re: [Qemu-devel] Default cache mode, Alexander Graf, 2011/06/29
Re: [Qemu-devel] Default cache mode, Stefan Hajnoczi, 2011/06/29