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Re: [Qemu-devel] Default cache mode
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] Default cache mode |
Date: |
Wed, 29 Jun 2011 16:12:06 +0200 |
User-agent: |
Mutt/1.5.17 (2007-11-01) |
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.
- 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 <=
- 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, Anthony Liguori, 2011/06/29
Re: [Qemu-devel] Default cache mode, Alexander Graf, 2011/06/29