On Fri, 29 Aug 2008, Kyle McDonald wrote:
>>
> What would one look for to decide what vdev to place each LUN?
>
> All mine have the same Current Load Balance value: round robin.
That is a good question and I will have to remind myself of the
answer. The "round robin" is good because that means that there are
two working paths to the device. There are two "Access State:" lines
printed. One is the status of the first path ('active' means used to
transmit data), and the other is the status of the second path. The
controllers on the 2540 each "own" six of the drives by default (they
operate active/standby at the drive level) so presumably (only an
assumption) MPxIO directs traffic to the controller which has best
access to the drive.
Assuming that you use a pool design which allows balancing, you would
want to choose six disks which have 'active' in the first line, and
six disks which have 'active' in the second line, and assure that your
pool or vdev design takes advantage of this.
For example, my pool uses mirrored devices so I would split my mirrors
so that one device is from the first set, and the other device is from
the second set. If you choose to build your pool with two raidz2s,
then you could put all the devices active on the first fiber channel
interface into the first raidz2, and the rest in the other. This way
you get balancing due to the vdev load sharing. Another option with
raidz2 is to make sure that half of the six disks are from each set so
that writes to the vdev produce distributed load across the
interfaces. The reason why you might want to prefer load sharing at
the vdev level is that if there is a performance problem with one
vdev, the other vdev should still perform well and take more of the
load. The reason why you might want to load share within a vdev is
that I/Os to the vdev might be more efficient.
Bob
======================================
Bob Friesenhahn
[EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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