On Mon, 11 Jan 2010, Anil wrote:
ZFS will definitely benefit from battery backed RAM on the
controller as long as the controller immediately acknowledges cache
flushes (rather than waiting for battery-protected data to flush to
the
I am little confused with this. Do we not want the controller to
ignore these cache flushes (since the cache is battery protected)?
What did you mean by acknowledge? If it acknowledges and flushes
the cache, then what is the benefit of the cache at all (if ZFS
keeps telling to flush ever few seconds)?
We want the controller to flush unwritten data to disk as quickly as
it can regardless of whether it receives a cache flush request. If
the data is "safely" stored in battery backed RAM, then we would like
the controller to acknowledge the flush request immediately. The
primary benefit of the battery-protected cache is to reduce latency
for small writes.
I use mostly DAS for my servers. This is a x4170 with 8 drive bays.
So, what's the final recommendation? Should I just RAID 1 on the
hardware and put ZFS on top of it?
Unless you have a severe I/O bottleneck through your controller, you
should do the mirroring in zfs rather than in the controller. The
reason for this is that zfs mirrors are highly resilient, intelligent,
and resilver time is reduced. Zfs will be able to detect and correct
errors that the controller might not be aware of, or be unable to
correct.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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