[Gluster-users] Optimal shard size & self-heal algorithm for VM hosting?

Krutika Dhananjay kdhananj at redhat.com
Thu Feb 16 10:22:55 UTC 2017

On Wed, Feb 15, 2017 at 9:38 PM, Gambit15 <dougti+gluster at gmail.com> 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.


> Thanks in advance,
> Doug
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