On Mon, 11 Jan 2010, Anil wrote:
What is the recommended way to make use of a Hardware RAID
controller/HBA along with ZFS?
Does it make sense to do RAID5 on the HW and then RAIDZ on the
software? OR just stick to ZFS RAIDZ and connect the drives to the
controller, w/o any HW RAID (to benefit from the batteries). What
will give the most performance benefit?
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
disks). There will be benefit as long as the size of the write data
backlog does not exceed controller RAM size.
The notion of "performance" is highly arbitrary since there are
different types of performance. What sort of performance do you need
to optimize for?
I think that the best performance for most cases is to use mirroring.
Use two controllers with battery-backed RAM and split the mirrors
across the controllers so that a write to a mirror pair results in a
write to each controller. Unfortunately, this is not nearly as space
efficient as RAID5 or raidz.
Many people will recommend against using RAID5 in "hardware" since
then zfs is not as capable of repairing errors, and because most RAID5
controller cards use a particular format on the drives so that the
drives become tied to the controller brand/model and it is not
possible to move the pool to a different system without using an
identical controller. If the controller fails and is no longer
available for purchase, or the controller is found to have a design
defect, then the pool may be toast.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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