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

[Krutika Dhananjay]

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.

-Krutika


>
> Thanks in advance,
> Doug
>
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