[Gluster-users] Performance question

[Brian Candler]

On Mon, Feb 13, 2012 at 12:37:10AM +0100, Arnold Krille wrote:
> 1) two nodes, two bricks, 2) two nodes, four bricks and 3) three 
> nodes, 6bricks.

Are these distributed only, or replicated?

If I understand it right (and I'm quite new to gluster myself), whenever you
do a read on a replicated volume, gluster dispatches the operation to both
nodes, waits for both results to come back, and checks they are the same
(and if not, works out which is wrong and kicks off a self-heal operation)

http://www.youtube.com/watch?v=AsgtE7Ph2_k

And of course, writes have to be dispatched to both nodes, and won't
complete until the slowest has finished.  This may be the reason for your
poor latency.

I don't know how dbench operates - is it entirely single-threaded or does it
attempt to run concurrent operations to simulate concurrent clients?  I
would except to get higher throughput in the latter case.

> I find it remarkable that the local disk is faster by a factor of two in 
> throughput and faster by a factor of ten(!) in latency.

As well as trying non-replicated gluster, I think you should try NFS as a
baseline for what dbench might be able to achieve on a network-attached
filesystem.

As Scotty used to say, "ya canna change the laws of physics", or something
like that.

Regards,

Brian.