Re: Changing disks in RAID-5 -- MIDRANGE-L

I think you can buy the 4 Gig drives for about $100, they aren't worth anything. We added some to our 820 for an LPAR about 2 years ago for around $400. Didn't need them when we moved to our 810. We got them from IBM (ICC) used.

Marc Rauzier wrote:

Le jeu. 02 déc. 2004 13:48:24, MITTELHEISSER Jean Claude écrivait:
Hi all,
Hello Jean-Claude
We have a 620 in V4R2 with 6 disks (4.19 Gb #6807), 1 RAID-5 controller (#2741) and 1 tape unit (1/4 inch 2.5 Gb #6481). It will die at end 2005. So we don't want to make too much investments, but we have to add some disk storage. We will ask IBM if we can add new cards. But we thought about replacing some cards by others with higher volume (perhaps 8.58 Gb). At that level, is it possible to disable a 4.19 Gb disk, unmount it, mount a new 8.58 Gb one, activate it under READ-5 and repeat the operation for a second one ? Or is it easier to backup the whole machine, stop it, replace some disks and restart from tapes ?

In a RAID5 set, you cannot mix disks with different capacities. The 2741 cannot manage less than 4 drives in a RAID5 set. So, if you want to keep a RAID5 protection, your only choice is to move from your current situation to a full RAID5 set with 6 8,58 GB disks. You can do it by replacing one 4GB drive (or two or three depending the disk space used) by one 8GB drive (or two or three) at a time. But the RAID5 must be stopped before the whole process and cannot be restarted after the whole replacing process is finished.

Another point : after this operation, your disks will be unbalanced and I cannot remember if the STRASPBAL was available in V4R2 (I don't think so). This is not the case if you perform a full backup/restore, which stays anyway IMHO more dangerous.

With you current solution, you have 5*4,19 GB equal 20,95 GB of usable space. If you replace all the drives with a 8,58 GB drives and keep a RAID5 protection, you will have 42,9 GB of usable space.

But, for any solution you will use, don't forget to double backup your system and be ready to perform a full restore !
Thanks.
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