On Tue, 27 Apr 2010, Roy Sigurd Karlsbakk wrote:
I have a test system with snv134 and 8x2TB drives in RAIDz2 and
currently no Zil or L2ARC. I noticed the I/O speed to NFS shares on
the testpool drops to something hardly usable while scrubbing the
pool.
How can I address this? Will adding Zil or L2ARC help? Is it
possible to tune down scrub's priority somehow?
Does the NFS performance problem seem to be mainly read performance,
or write performance? If it is primarily a read performance issue,
then adding lots more RAM and/or a L2ARC device should help since that
would reduce the need to (re-)read the underlying disks during the
scrub. Likewise, adding an intent log SSD would help with NFS write
performance.
Zfs scrub needs to access all written data on all disks and is usually
disk-seek or disk I/O bound so it is difficult to keep it from hogging
the disk resources. A pool based on mirror devices will behave much
more nicely while being scrubbed than one based on RAIDz2.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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