[Sheepdog] Object node affinity

[Liu Yuan]

On 05/10/2012 06:22 PM, Matthew Law wrote:

> On Thu, May 10, 2012 11:00 am, HaiTing Yao wrote:
>> There is no the affinity. The data's storage location depends on its hash
>> value. It perhaps resides on the host created the VM, but there is no
>> affinity.
>>
>> You can try the object cache. The cache will keep data on local host.
>>
>> If there is one local copy,  request will read the copy at first and will
>> not retieve the remote copies.
> 
> Thanks. Is there any danger of the cached objects becoming stale?  If not
> it seems a good option for those with small clusters that are not on low
> latency, high bandwidth networks.
> 


Nope, at least by design, cached objects will always be the freshest
one. Though those cached objects are supposed to be flushed to the
cluster storage and would survive the host node crash, but you will
still be risking yourself to lose those 'updates' that haven't been
flushed yet in a disaster that the disk never comes back. You can
analogize object cache with kernel's page cache, and difference is that
data is cached into local disk instead of memory.

Thanks,
Yuan