ZFS/compression/performance

[Jeremy Chadwick]

On Wed, Oct 12, 2011 at 09:37:10AM -0700, David Brodbeck wrote:
> On Wed, Oct 12, 2011 at 5:02 AM, Johannes Totz <jtotz at imperial.ac.uk> wrote:
> 
> > I just did a simple write test yesterday:
> >
> > 1) 6 MB/sec for gzip, 1.36x ratio
> > 2) 34 MB/sec for lzjb, 1.23x ratio
> >
> > I'll stick with lzjb. It's good enough to get rid of most of the
> > redundancy and speed is acceptable.
> >
> 
> That's what we use on our text-heavy filesystems on our OpenSolaris server.
>  (We work with large text corpora, so we have hundreds of gigabytes of pure
> text.)  My benchmarks showed the performance hit for reads is nonexistent
> when viewed over NFS, and the performance hit for writes is relatively
> small...plus we don't write to that filesystem much.  We see about 1.5x
> compression overall, with a little over 2x on some datasets that are
> particularly compressible.

That might be the case on OpenSolaris but the performance hit on
FreeBSD RELENG_8 is very high -- enough that enabling compression (using
the defaults) causes stalls when I/O occurs (easily noticeable across
SSH; characters are delayed/stalled (not buffered)), etc..

The last time I tried it on RELENG_8 was right after ZFSv28 was MFC'd.
If things have improved I can try again (I don't remember seeing any
commits that could affect this), or if people really think changing the
compression model to lzjb will help.

Another point: I haven't tinkered with compression on our Solaris 10
machines at work so I don't know if it performs better, equal, or worse
than FreeBSD or OpenSolaris.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                   Mountain View, CA, US |
| Making life hard for others since 1977.               PGP 4BD6C0CB |