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

[Matthew Law]

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.

Hope that helps,


Matt.