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
