[WBEL-users] RAID

[Kirby C. Bohling]

On Tue, Mar 08, 2005 at 04:23:54PM -0700, Arif Gangji wrote:
> 
> Have there been any tests done regarding hard drive failures and recovery on
> a sw RAID system with WBEL?
> 
> i.e. how easy is it to get your data replicated back onto a new drive if 1
> fails?  Does it just continue running off the second drive?

It's fairly trivial depending on the nature of the failure.  If you
have a hot spare in the box and mdadm.conf is configured correctly
it'll just start the remirror for you (you have to be running
mdmonitor).

However, in my experience, we've had several instances where our
SCSI card driver died a horrible death on a drive failure.  Which
locked up the SCSI chain, which in turn locked up the SCSI
subsystem.  Which left you in a fairly serious shape.  The box had
to be hard rebooted.  That was a problem with the ServRAID adaptors
w/ the 4.8n (where I believe n=4) drivers.

Mostly you just run this:
mdadm --add /dev/md0 /dev/sdc1

If you have hotswap SCSI cages, you might have to do the right thing
to recognize the drive has been replaced.  Then run something like
the above command.  Your mirror is rebuilt while you wait.

Fiddle with /proc/sys/dev/raid/speed_limit_{min,max} to control how
fast or slow the rebuild can go.

About the only real downer with software raid is that if a box
crashes, all of the software RAID mirrors have to be rebuilt.  Which
is a serious drag.  A good hardware controller should mitigate that
(battery backed up RAM and all that).

	Thanks,
		Kirby


> 
> -----Original Message-----
> From: whitebox-users-bounces at beau.org
> [mailto:whitebox-users-bounces at beau.org]On Behalf Of Vic
> Sent: Tuesday, March 08, 2005 4:14 PM
> To: whitebox-users at beau.org
> Subject: Re: [WBEL-users] RAID
> 
> 
> > One thing to consider is that those cheaper cards are nothing
> > more than ide controllers with software raid. Do you have the ide
> > ports on your motherboard free?  IF so just use the kernel's
> > software raid.  If the card is recognized as a regular set of ide
> > ports..i would just use the kernel's software raid..:)
> 
> That's probably good advice even if the card does have hardware RAID; it
> gives you a good deal of future-proofing should the card ever go belly-up
> & you need data off those drives...
> 
> Vic.
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