[Sheepdog] [PATCH v2 10/10] farm: add a documentation for farm internals

[Liu Yuan]

On 12/22/2011 03:10 PM, Dietmar Maurer wrote:

>> +Farm has a working directory that is the ground for storing objebts
>> +from Sheepdog I/O requests. That being said, the I/O performance for Vm
>> +Guests would be practically the same as Simple Store.
> 
> I don't really understand that. You need to compute the sha1 hash and compress
> all data - so how can you get the same I/O performance?
> 


Farm only computes the sha1 hash and compress all data in order to
'cache' them, *only* when the snapshot is taken, triggered either by
recovery code or user.

For other cases, for e.g, serving normal I/O requests, use simple
pread/pwrite for object storing like Simple Store, except that
farm.write() do a bit bookkeeping.

Thanks,
Yuan