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Breaking disk mirror / replacement after testing

Hans Beyer
Occasional Contributor

Breaking disk mirror / replacement after testing

If I have a DL380 with 3 x 36GB drives in a Mirrored set with 1 spare; if I take SCSI ID 0 out; let SCSI 1 & the spare rebuild, apply patches; after testing system and all is working correctly; what is the best way to re-insert SCSI 0 into the array without reverting back to the original configuration on that particular drive which was part of the original mirror?
Uwe Zessin
Honored Contributor

Re: Breaking disk mirror / replacement after testing

It is good that you're asking before trying it out ;-)
One of my colleagues destroyed one of my OS disks because he plugged it in while the server was powered off and the mirroring went into the 'wrong direction' - goodbye data :-(

Works fine if you put the disk with the old data in while the system is running.

I guess you did not really 'break' the mirror, just pulled the disk during power-off. Otherwise it would mean you've used the ACU to split the RAID set into two independed disks and had to revert that operation.

Re: Breaking disk mirror / replacement after testing

Agree, mostly with Uwe.

Power down server.
Remove disk 0 or 1.
Power up.
let it rebuild to the spare.
Make your updates.
if everything is ok.
Hotplug the missing disk.

The META data is time stamped.
If you coldplug the missing disk
The smart array will rebuild from the latest time stamp to oldest.

Why things went wrong for Uwe's colleage.
Your guess is as good as mine.

I recommend
Cold remove.
Hot plug.

Beware, there's allways a risk.

Ensure you have got a good backup.
Use System Management home page, ACU and ADU
to ensure that all disks are ok, and ID's is correct.

From generation 6 smart arrays and some of the later smart arrays, it is possible to do an on-line spilt and recombine.
But I have no idea, how it behave with the spare disk.

Hans Beyer
Occasional Contributor

Re: Breaking disk mirror / replacement after testing

That would be correct, I am not planning on using the ACU to split or break the mirror; just removing disk0, allowing disk1 and disk2 (spare) to rebuild then doing the updates. If all goes well then inserting disk0 back into the mirror (hot) which should just become part of the updated set of disks again.
If things donâ t go well I will be powering the server down, removing both disk1 and disk2, inserting disk0, powering up the system, then putting disk1 and disk2 back into the mix.
Any other recommendations or input is welcome!

Re: Breaking disk mirror / replacement after testing

A good backup and recovery plan is recommended.

Good luck.