mfi - setting up disks

[Dag-Erling Smørgrav]

Niklas Saers <niklas at saers.com> writes:
> In the SuperMicro system where I had problems with the mpt controller,
> I switched it for a mfi-based controller. I had it set up with 36x
> RAID0 volumes with each their own disk (no way to access the disk
> otherwise I found), and added them to a ZFS system. The numbering
> became a bit weird, so I pulled the disks out one by one and put them
> back to figure out and note down what disk number was in what
> slot. Only test data on my ZFS volume, so I didn't mind that crashing.

You can wire down SCSI buses and disks in /boot/device.hints so each
disk always gets the same device number regardless of the order in which
the disks spin up.  The syntax is documented in /sys/conf/NOTES (search
for "SCSI DEVICE CONFIGURATION").  It's a CAM feature, and mfi uses CAM,
so I *think* it should work for mfi as well, but what you'll actually be
wiring down are mfi volumes, not individual disks, so it's up to you to
assign the right disk to the right volume.

I am very close to suggesting that you just let the controller handle
the RAID part of things and just build your zfs pool on top of that,
i.e. use mfiutil to divide your disks into 5 x 6+1, 5 x 5+2 or 7 x 4+1
volumes plus one spare, and use each volume as a separate vdev in your
zfs pool.  You may lose a small amount of performance, and rebuilds will
be slower, but the main argument in favor of zfs, the write hole, is
moot if your controller has battery-backed cache.

DES
-- 
Dag-Erling Smørgrav - des at des.no