[olug] The "other" raid utility usage

[Matthew G. Marsh]

On Tue, 22 Apr 2003, Nick Walter wrote:

> Hmm, interesting.  Hot swapping with a hardware RAID controller is old
> news, but I've never heard of doing it with software RAID on linux.  I'd
> be scared to pull a drive out of a running array for fear of what
> bizarre conniptions the SCSI driver would have.  Did you have to use a
> special utility to deactivate the drive first?

Nope. That was the interesting part. Now bear in mind that these drives
are installed into an external drive array. But the SCSI subsystem did not
hiccup. One minor problem is that unless you probe the drive itself you
won't see the array message. But you can spin a drive down using the
sgutils below (along with a whole lot of other interesting things...)

But I figured I had better test the array so that when I do have a drive
fail I know I can swap it out without rebooting or deactivating the array
(which is kind of the point of a RAID array IMHO).

> Nick Walter
>
>
> On Tue, 2003-04-22 at 11:28, Matthew G. Marsh wrote:
> > OK - the posting on the software raid stuff done at the last meeting by
> > Adam got me wondering. Last time I played with SoftRaid was back in
> > 2.1.{something} and it was ok but not amazing.
> >
> > LSS - raidtools would not compile (no surprise there as it is a rathead
> > util) so I found one called mdadm.
> >
> > http://www.cse.unsw.edu.au/~neilb/source/mdadm/
> >
> > I am quite happy. This compiles static! and is only 854228 when compiled
> > static. Tested it without libraries and it worked fine.
> >
> > It also will do everything the raidtools will plus it has a daemonized
> > monitor mode that sends email or gens SNMP traps for array messages...
> >
> > Also found some scsi generic utils that enable spinup/spindown and a whole
> > lot of other neat things (I run pretty much only SCSI on my servers) and
> > so I figured maybe I would post what I played with FYI.
> >
> > SG3 - http://www.torque.net/sg/u_index.html  (sg3_utils-1.03.tgz)
> >
> > First off - array = (10) 18.3G UW drives in a hardware rack (IBM EXP15)
> >
> > Using a SymBios UW controller (happened to have handy on the Compaq server
> > and it was not even in use...)
> >
> > 1. Created partitions (not needed actually - see docs on mdadm)
> > 	1.1 (1) per drive - full size
> > 2. Created RAID5 array
> > 	mdadm --create /dev/md0 --level=5 --raid-devices=10 /dev/sd[a-j]1
> > 3. Formatted as ext3
> > 	mke2fs -b 1024 -j -v -L "DATA" /dev/md0
> > 4. Mounted array
> > 	mount /dev/md0 /data
> >
> > Then decided to play with the system to see how to recover the array on
> > failure (thanks paul...)
> >
> > Pulled out a drive.
> > OK - degraded array.
> > Put back in the drive.
> > Hmmm - no nothing happened.
> > fdisk the drive - no such device - whoops.
> > went and found sg3 utils
> > used them to spin up drive  sg_start /dev/sg2 1
> > fdisk works fine - partition still exists
> > now used mdadm to fail, remove, and add back in drive
> > 	mdadm /dev/md0 -f /dev/sdc1 -r /dev/sdc1 -a /dev/sdc1
> > Adn the array starts to rebuild.
> >
> > Cool!
> >
> > HTH.
> >
> > --------------------------------------------------
> > Matthew G. Marsh,  President
> > Paktronix Systems LLC
> > 1506 North 59th Street
> > Omaha  NE  68104
> > Phone: (402) 553-2288
> > Email: mgm at midwestlinux.com
> > WWW:  http://www.midwestlinux.com
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--------------------------------------------------
Matthew G. Marsh,  President
Paktronix Systems LLC
1506 North 59th Street
Omaha  NE  68104
Phone: (402) 553-2288
Email: mgm at midwestlinux.com
WWW:  http://www.midwestlinux.com
--------------------------------------------------