Re: Optimal shard size & self-heal algorithm for VM hosting?

[Krutika Dhananjay <kdhananj@xxxxxxxxxx>]

On Wed, Feb 15, 2017 at 9:38 PM, Gambit15 <dougti+gluster@xxxxxxxxx> wrote:

Hey guys,

 I keep seeing different recommendations for the best shard sizes for VM images, from 64MB to 512MB.

What's the benefit of smaller v larger shards?

I'm guessing smaller shards are quicker to heal, but larger shards will provide better sequential I/O for single clients? Anything else?

That's the main difference. And also smaller shards provide better brick utilization and distribution of IO in distributed-replicated volumes as opposed to larger shards.

I also usually see "cluster.data-self-heal-algorithm: full" is generally recommended in these cases. Why not "diff"? Is it simply to reduce CPU load when there's plenty of excess network capacity?

That's correct. diff heal requires rolling checksum to be computed for every 128KB chunk of the file on both source and sink bricks, which is CPU intensive, potentially affecting IO traffic.

-Krutika
 

Thanks in advance,

Doug

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