Il 09/01/2013 11:36, Liu Yuan ha scritto: >> But why is it useful to force-disable writeback caching? Do you have >> > any performance numbers? > This is not related to performance. What I want is to allow users to > choose Sheepdog cache mode (writethrough/writeback/directio) from cache=xxx. > > Obviously writeback mode show much better write performance over > writethrough cache in Sheepdog. NOTE: writethrough cache in Sheepdog is > a readonly cache which is always consistent with cluster data thus need > no flush at all. This is to boost read performance for read intensive > Guest over Sheepdog iamges.
Ok, so the questions are (compared to older QEMU's writethrough mode): 1) how slower is QEMU's emulated-writethrough mode for writes, due to the extra requests? 2) how slower is QEMU's writeback mode for reads, due to the different structure of the cache? Paolo
