Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics

[Kevin Wolf]

Am 09.01.2013 11:36, schrieb Liu Yuan:
> On 01/09/2013 06:25 PM, Paolo Bonzini wrote:
>> 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.

The question was which effects these modes have, and especially what the
user-visible differences between writeback+flush and writethrough cache are.

> 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.

This is the definition of a writethrough cache.

Kevin