[Gluster-users] Replica with non-uniform bricks

[Jeff Darcy]

On 08/13/2012 04:16 PM, Brian Candler wrote:
> On Mon, Aug 13, 2012 at 06:03:36PM +0200, s19n wrote:
>>  So the question is: what is the expected behaviour when two bricks
>> with different sizes are coupled to form a replica? Will the larger
>> brick keep accepting writes even after the smallest brick has been
>> filled up?
> 
> I haven't tested, but I'd expect ENOSPC when the smaller one files up.
> 
> I'd be inclined to split the larger server into two volumes: one the same
> size as the smaller server, to form a replica set, and put the remaining
> space in a single-volume brick for use as scratch space, backups, or
> whatever.

I second that.  I haven't tested this myself, but I don't see any special
handling of ENOSPC in the AFR code.  I strongly suspect that what you'd see is
an initial write error on the smaller replica, followed by repeated self-heal
failures for the same reasons.  Ick.  Just be aware that you'd be sharing
resources (e.g. disk heads) between the artificially small replica and the
scratch space, so using both simultaneously might cause a significant
performance degradation.