[Sheepdog] some questions about sheepdog

MORITA Kazutaka morita.kazutaka at lab.ntt.co.jp
Thu Aug 4 19:25:41 CEST 2011

At Thu, 4 Aug 2011 09:06:14 +0000,
Frank Doege wrote:
> Hi List,
> At first, this really looks like a great project and I feel also that its very alive, so I am planning to do a test installation of sheepdog storage backed
> I have already read what I could find about this project however there is not so much documentation out there yet.
> I have a couple of questions, I would appreciate if someone could enlighten me :-)
> 1.
>  sheepdog needs at least two storage nodes to work, data is distributed like in a RAID1 therefore I always need 
> the double of the capacity I plan to use for kvm guests, is there a Parity option that works like RAID5 ?

No, and there is no plan to support it now, sorry.  But if someone
would implement the feature, I'd happily merge it into Sheepdog.

> 2. 
> Does anyone has some performance numbers, with two nodes and 8HDD SAS Raid5 dual Gbit network bond
> What can I get for an estimated performance ? What is the bottleneck here, the network or the disks ?

I have some numbers in the slides I presented before:
The bottleneck was the disk I/O In these tests.

However, the results strongly depends on the environment and the
workloads, so I'm not sure what the bottleneck would be on your

> 3. 
> Sheepdog uses the network to connect to the nodes, I guess it balances data in chunks over all available nodes, in the moment
> It stores each chunk on a node and a copy on another node, is this rotated over all nodes or is each image fixed on two nodes ?

Sheepdog uniformly distributes chunks to all over the nodes.

> 4.
> As sheepdog uses the network as a transport medium am how high is the latency, is this an issue in production networks ?

If your KVMs do many disk syncs to Sheepdog volumes, the network
latency could be a problem.  But otherwise, I think Sheepdog
performance is good.



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