[Gluster-users] GlusterFS performance questions

[Ed W]

On 14/03/2011 22:18, Alexander Todorov wrote:
> Hello folks,
> I'm looking for GlusterFS performance metrics. What I'm interested in
> particular is:
> 
> * Do adding more bricks to a volume make reads faster?
> * How do replica count affect that?

Although no one seems to be really talking about performance in these
terms, I think the limiting factor is usually going to be network
latency.  In very approximate terms, each time you touch a file in
Glusterfs you need to ask every other brick for it's opinion as to
whether you have the newest file or not.  Therefore your file IO/sec is
bounded by your network latency...

So I would presume that those who get infiniband network hardware and
it's few uS latency times see far better performance than those of us on
gigabit and the barely sub millisec latency that this entails?

So I suspect you can predict rough performance while changing the
hardware by thinking about how the network constrains you.  eg consider
your access pattern, small files/large files, small reads/large reads,
number of bricks, etc

Note it doesn't seem popular to discuss performance in these terms, but
I think if you read through the old posts in the lists you will see that
really it's this network latency vs required access patterns which
determine whether they feel gluster is fast/slow?

To jump to a conclusion, it makes sense that large reads on large files
do much better than accessing lots of small files...  If you make the
files large enough then you start to test the disk performance, etc

Good luck

Ed W