On Wed, 17 Nov 2010, LEES, Cooper wrote:
Zfs Gods,
I have been approved to buy 2 x F20 PCIe cards for my x4540 to
increase our IOPs and I was wondering what would be the most benefit
to gain extra IOPs (both reading and writing) on my zpool.
To clarify, adding a dedicated intent log (slog) only improves
apparent IOPS for synchronous writes such as via NFS or a database.
It will not help async writes at all unless they are contending with
sync writes. A l2arc device will help with read IOPS quite a lot
provided that the working set is larger than system RAM yet smaller
than the l2arc device. If the working set is still much larger than
RAM plus l2arc devices, then read performance may still be
bottlenecked by disk.
Take care not to trade IOPS gains for a data rate throughput loss.
Sometimes cache devices offer less throughput than main store.
There is little doubt that your pool would support more IOPS if it was
based on more vdevs, containing fewer drives each.
I doubt that anyone here can adequately answer your question without
measurement data from the system taken while it is under the expected
load.
Useful tools for producing data to look at are the zilstat.ksh and
arc_summary.pl scripts which you should find mentioned in the list
archives.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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