Hi,
On a busy NFS server, performance tends to be very modest for large amounts
of small files due to the well known effects of ZFS and ZIL honoring the
NFS COMMIT operation[1].
For the mature sysadmin who knows what (s)he does, there are three
possibilities:
1. Live with it. Hard, if you see 10x less performance than could be and your
users complain a lot.
2. Use a flash disk for a ZIL, a slog. Can add considerable extra cost,
especially if you're using an X4500/X4540 and can't swap out fast SAS
drives for cheap SATA drives to free the budget for flash ZIL drives.[2]
3. Disable ZIL[1]. This is of course evil, but one customer pointed out to me
that if a tar xvf were writing locally to a ZFS file system, the writes
wouldn't be synchronous either, so there's no point in forcing NFS users
to having a better availability experience at the expense of performance.
So, if the sysadmin draws the informed and conscious conclusion that (s)he
doesn't want to honor NFS COMMIT operations, what are options less disruptive
than disabling ZIL completely?
- I checked the NFS tunables from:
http://dlc.sun.com/osol/docs/content/SOLTUNEPARAMREF/chapter3-1.html
But could not find a tunable that would disable COMMIT honoring.
Is there already an RFE asking for a share option that disable's the
translation of COMMIT to synchronous writes?
- The ZIL exists on a per filesystem basis in ZFS. Is there an RFE already
that asks for the ability to disable the ZIL on a per filesystem basis?
Once Admins start to disable the ZIL for whole pools because the extra
performance is too tempting, wouldn't it be the lesser evil to let them
disable it on a per filesystem basis?
Comments?
Cheers,
Constantin
[1]: http://blogs.sun.com/roch/entry/nfs_and_zfs_a_fine
[2]: http://blogs.sun.com/perrin/entry/slog_blog_or_blogging_on
--
Constantin Gonzalez Sun Microsystems GmbH, Germany
Principal Field Technologist http://blogs.sun.com/constantin
Tel.: +49 89/4 60 08-25 91 http://google.com/search?q=constantin+gonzalez
Sitz d. Ges.: Sun Microsystems GmbH, Sonnenallee 1, 85551 Kirchheim-Heimstetten
Amtsgericht Muenchen: HRB 161028
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Vorsitzender des Aufsichtsrates: Martin Haering
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