[Linux-cluster] Re: Why GFS is so slow? What it is waiting for?

[Bob Peterson]

On Sat, 2008-05-10 at 09:10 +0200, Klaus Steinberger wrote:
> How can I performance-tune GFS or make it any faster?
(snip)
>       Use -r 2048 on gfs_mkfs and mkfs.gfs2 for large file systems.

Actually, this is a delicate balance.  If you have too many resource
groups (RGs) then it spends a lot of time searching to find the
one it needs, but once it finds the RG, the bitmap search will be fast.
If you have fewer RGs, it will spend less time searching for the right
one, but the bitmaps for each will be bigger, so it will spend more
time searching the bitmap once it has been found.

I've written a performance enhancement to the "bitfit" algorithm for
GFS2 that increases the speed of bitmap searches, making it more speedy
to use fewer RGs with larger bitmaps.  That code could be back-ported to
GFS, but it hasn't been done yet.  Actually, there are a lot of
performance improvements done for GFS2 that COULD theoretically be
ported back to GFS, if someone took the time.  Perhaps I'll open an
RFE bugzilla and post any patches I come up with to the cluster-devel
mailing list.

Regards,

Bob Peterson
Red Hat Clustering & GFS