[Sheepdog] general question about sheepdog operation (block distribution)

[Miles Fidelman]

MORITA Kazutaka wrote:
> At Mon, 31 Oct 2011 09:07:25 -0000,
> Matthew Law wrote:
>> On Mon, October 31, 2011 2:17 am, Miles Fidelman wrote:
>>> Something that's not quite obvious from the documentation:
>>>
>>> How does Sheepdog spread blocks around when nodes have multiple disks?
>>> For example, on a 4-node cluster, where each node has 4 drives, is
>>> Sheepdog smart enough to replicate blocks in ways that protect against
>>> both individual drive failures, and node failures that take out 4 drives
>>> at a time?
>> Hi Miles,
>>
>> my understanding of sheepdog is that one would normally run a sheep daemon
>> per logical disk.  My testing has been by running a single sheep daemon
>> per linux md raid 10 device.  This is obviously overkill but suited my
>> setup and sheepdog's features at the time.
>>
>> The better solution for current sheepdog is to run one sheep daemon per
>> disk and use the failure zones which were recently introduced to tell
>> sheepdog 'where' the disks live so it does not place all copies of a block
>> of data on a single physical server.
> Yes, and Sheepdog uses the same zone id in the same node by default;
> dada will be replicated across nodes without any configuration.

Thanks guys.  (FYI - I currently run DRBD over a pair of nodes that each 
run md raid 10 - as I go to 4 nodes, I've  been looking at different 
ways of establishing a reliable storage environment that allows VMs to 
migrate.)


-- 
In theory, there is no difference between theory and practice.
In<fnord>  practice, there is.   .... Yogi Berra