Re: Quick question on Software RAID support.

From: Bill Davidsen (davidsen@tmr.com)
Date: Tue Feb 12 2002 - 23:10:55 EST


On Wed, 13 Feb 2002, Chris Chabot wrote:

> Alan Cox wrote:
> >>1) Does the Software RAID-5 support automatic detection
> >> of a drive failure? How?
> >>
> >
> > It sees the commands failing on the underlying controller. Set up a software
> > raid 5 and just yank a drive out of a bay if you want to test it
>
> This is also why software raid 5 + IDE is a bad combo. It has a high
> chance of locking up the IDE controller, and requiring you to power down
> & fix the system before reconstruction can commence. However with SCSI
> hot-swapable solutions, on-the-fly reconstruction after failure works
> perfectly.

>From personal experience software RAID is quite fast, and very reliable
regarding failures while running. If a disk fails the system drops back to
recovery, and after a new drive is added and `raidhotadd' is run it is
rebuilt.

The dark side of the force is that is a drive fails on boot, I have had
problems getting the system to boot (even when not the boot drive). The
system doesn't always recognize that there is a failed drive, and I've had
to build a new raid config with "failed disk" entries to get the system
up. Later version may be better at that (comments, please), I have not had
to address this in over a year, since most of my system are not taken down
unless they fall down.

-- 
bill davidsen <davidsen@tmr.com>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

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