[Gluster-users] AFR, writebehind, and debug/trace

[Peter Gervai]

On Mon, Jun 29, 2009 at 23:49, Barry Jaspan<barry.jaspan at acquia.com> wrote:
> I just got started with glusterfs.  I read the docs over the weekend and
> today created a simple setup: two servers exporting a brick and one client
> mounting them with AFR. I am seeing very poor write performance on a dd
> test, e.g.:
>
> time dd if=/dev/zero of=./local-file bs=8192 count=125000
>
> presumably due to a very large number of write operations (because when I
> increase the blocksize to 64K, the performance increases by 2x).  I enabled

I didn't want to enter these threads because I may sound a bit
pessimistic, but here's my experience with glusterfs.

I needed a simple NFS replacement at the moment (but I guess it's just
the same for any application with the exception that there aren't
alternatives).

With the kernel fuse module _everything_ was dirt poor, basically
useless. Replacing it with the glusterFS patched one improved
performance around 5-fold. Still, I have experienced useless write
performance below 64k block size (3MB/s in contrast to 60MB/s). I have
found no solution, apart from _not_ using writeback which slowed it
down to the half speed (around 2MB/s).

Read performance is excellent.

I am about to use iSCSI (linux at both ends, software components
only), which seem not to impose that problem.

I guess it's not glusterFS but FUSE, but I see no workaround for it.

-- 
 byte-byte,
    grin