Extending RAID 5

[Lennart Sorensen]

On Mon, May 26, 2008 at 04:38:36PM -0400, William O'Higgins Witteman wrote:
> I have a Dell PowerEdge 6800 server which is set up with 3 drives in a
> hardware RAID 5.  I need to increase storage capacity on this machine,
> and I have 3 more drives.  What do I do?
> 
> 1. Do I just plug in the drives hot and hope for the best? (I don't see
> how that could work.)
> 
> 2. Do I boot into the RAID utility and extend the existing RAID.  If
> this works, how do I explain to Linux what is happening?
> 
> 3. Do I boot into the RAID utility and extend the existing RAID and then
> reinstall?
> 
> Any advice would be appreciated - I didn't choose the server, and I
> don't know RAID.  Thanks.

I have never worked with Dell's raid.  I have worked with IBMs raid in
the past.

The requirement on the IBM ServeRaid was:

Hotplug the drives (this was for hotplug drive bays)

Go into the raid management utility (IBM has a java based management
tool that works on linux)

Expand the raid5 onto the new devices

Wait for it to complete

Reboot the system so linux can see the new size of the device

Do whatever you have to do to partition tables and filesystem sizes to
take advantage of the extra space.

I believe the is work being done recently to let linux recognize volume
size changes at runtime, which would elliminate the reboot step.

Of course some hardware raid controllers can't even resize a raid in
which case you are down to 'backup, recreate, restore' which really
sucks.  Some can only resize offline, which means reboot to the raid
utility, resize, then boot back to linux and do the partition/filesystem
work.  The serveraid did it online which was nice since it reduced the
downtime to normally only a few minutes.

-- 
Len Sorensen
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