Am 08.01.2013 10:45, schrieb Liu Yuan: > On 01/08/2013 05:40 PM, Stefan Hajnoczi wrote: >> Otherwise use sheepdog writeback and let QEMU block.c decide when to >> flush. Never use sheepdog writethrough because it's redundant here. > > I don't get it. What do you mean by 'redundant'? If we use virtio & > sheepdog block driver, how can we specify writethrough mode for Sheepdog > cache? Here 'writethrough' means use a pure read cache, which doesn't > need flush at all.
A writethrough cache is equivalent to a write-back cache where each write is followed by a flush. qemu makes sure to send these flushes, so there is no need use Sheepdog's writethrough mode. Kevin