On 04/04/2012 01:00 AM, MORITA Kazutaka wrote: > At Mon, 2 Apr 2012 16:21:11 +0800, > Liu Yuan wrote: >> >> From: Liu Yuan <tailai.ly at taobao.com> >> >> We async flush dirty object as default to achieve the best performance. >> If users prefer strong consistency over performance, users can launch >> sheep with -S or --sync option. >> >> We need async flush because: >> 1) some APP are responsive time sensitive, the writeback of dirty bits in >> the guest will mostly hurt RT because guest need to await its completion. >> This is a considerably long operation in the sheep cluster. >> 2) some APP are just memory and CPU intensive, has little of concern of disk >> data. (For e.g, just use disk to store logs of APP) >> 3) People simply prefer performance over consistency. > > Sheepdog is a block device storage. This kind of feature must NOT be > default. In addition, we had better show a warning about a risk of > reading old data, which could cause a filesystem corruption, when > users enable this feature. > Okay, I'll submit a patch to make it optional. But in which way we'll risk to read stale data? Guests always try to read objects from cache with cache enabled, IMO. -- thanks, Yuan |