Re: Changing disks in RAID-5

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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-- 
Cordialement/Best regards
Marc Rauzier

Opinions I stated here are my own.