> My Boss wants to pull out a drive, and put an unformatted one in and see
how
> it rebuilds!
> A realistic test for the dark day.... The external drive is all data. OS
is
> inside...
> (does this matte?)
It sounds like your Compaq unit is a storage cabinet, giving you two
SCA backplanes, and you use the NCR controllers, doing your RAID in
software.
The potential problem isn't so much in whether it rebuilds or not, but
if the hot-swapping works or not. The SCA backplanes give you the
potential to get the drive on and off of the SCSI bus without glitches,
but there's more to it than that.
The drivers for the controllers that you're using have to support
hot-swapping as well. The Linux Software-RAID howto says:
(begin quote)
"If you want to play with this, you should know about SCSI and RAID
internals anyway. So I'm not going to write something here that I can't
verify works, instead I can give a few clues:
Grep for remove-single-device in linux/drivers/scsi/scsi.c
Take a look at raidhotremove and raidhotadd
Not all SCSI drivers support appending and removing devices. In the 2.2
series of the kernel, at least the Adaptec 2940 and Symbios NCR53c8xx
drivers seem to support this, others may and may not. I'd appreciate if
anyone has additional facts here... "
(end quote)
So it sounds like it's sort of a dicey operation. I'd at least want to
try it in the middle of the night (with backups, of course) before I
risked doing it during the day in front of the boss. The best thing would
be to have tried it before it was put into production. : )
Now, with a hardware RAID card, it's a different story - all of that is
handled on the card, and the card is specifically built to handle it. My
guess is that a hardware RAID card would only cost a fraction of what
you've already invested into drives and the enclosure, a dual-channel U2W
Mylex card starts out under $200, and of course they work their way up.
And having on-board cache makes it that much nicer.
Oh, there is one potential problem that I've run into with hardware RAID
controllers - some of the nicer ones have a buzzer on the board to alert
you to a problem, but some (like several AMI MegaRAID controllers) don't
have a way to turn off the buzzer during the rebuild, so if you do it in a
working environment, you have to tape some cotton over the buzzer to keep
your coworkers from getting headaches. ; )
steve
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