[Gluster-devel] Scaled down a bit.

Krishna Srinivas krishna at zresearch.com
Wed Nov 28 18:15:07 UTC 2007

On Nov 28, 2007 11:11 PM, Chris Johnson <johnson at nmr.mgh.harvard.edu> wrote:
> On Wed, 28 Nov 2007, Kevan Benson wrote:
> > Chris Johnson wrote:
> >>      Hi again.
> >>
> >>      I've scaled everything way back as was suggested.  I'm also using
> >> a dd file read as a test rather than iozone.  I have one brick on the
> >> server mounted on the client, that's it.  Using time dd I get between
> >> 260 to 285 MS to read a 24 MB file.  Doing the same thing with NFS I
> >> get about 20 to 30 MS less but I can live with that.

OK, noted. I am guessing this is because of user space overhead.

> >>
> >>      I tried with and without io-threads on the server end.  No
> >> noticable change either way.  I've read with io-threads is supposed to
> >> do.  I had 8 threads defined.  What does it do and does it make a
> >> different which side it's on, client or server?
> >
> > io-threads is supposed to speed up serving of files when multiple files are
> > requested at the same time (so dd won't trigger any benefits from it at all,
> > being a single request).  I.e. In situations on the server where it would be
> > blocking on new requests until finished with the current request, io-threads
> > allows another thread to handle the request for better response and
> > performance (at least that's how I understand it).

Correct. When multiple processes request for multiple files, performance gain
will be significant.

> >
> > As another email a few days ago stated, io-threads on the client side will
> > have little or no effect.

I had observed that client side io-threads also improves response time.

>       Ah ha!  Ok, tnx.
> >
> >>      I also tried the io-cache on the client side.  MAN does that
> >> work.  I had a 256 MB cache defind.  A reread of my 24 MB file took 72
> >> MS.  I don't think it even bothered with the server much.  I need to
> >> try that on the server.  Might help if a bunch of computer nodes
> >> hammer on the same file at the same time.
> >
> > Careful with io-cache and io-threads together, depending on where you define
> > it (I think), the cache is per-thread.  so if you have 8 threads and a 256 MB
> > cache defined, be prepared for 2 GB of cache use...
> >

No, If you define one io-cache translator there is only one cache. All the
threads will refer to the same io-cache translator with which it is associated


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