OT: Adding more disks to hardware RAID 5

gdstaples wrote on 12/10/2005, 10:54 AM
I have three 300GB drives configured with a hardware RAID card in RAID five with one partition at 558GB. Is there any danger to existing data in adding a 4th or 5th drive to the RAID? As I understand it, the more drives one adds to the RAID 5 the more efficient it becomes in terms of overhead.

Thanks,
Duncan

Comments

gdstaples wrote on 12/10/2005, 2:04 PM
Has anyone successfully added an additional drive to an existing RAID 5 configuration containing data without data corruption or loss? Trying to clarify my question.

Duncan
richard-courtney wrote on 12/10/2005, 2:11 PM
We use 4 drives in a RAID 5 config and have had 1 drive fail
and once the bad drive is replaced it rebuilds itself. Using 3Com
raid controller.

Your controller manual should explain those magic numbers.
Each drive is 200G and yields 600G (a percentage is used from
each drive to create the redundancy, that is why not 800G).
gdstaples wrote on 12/10/2005, 2:36 PM
Yes, at 3 drives you lose 33% and at 4 you lose 25% according to the info I have read.

My question was more about adding a 4th drive to a 3 drive raid. Not necessarily rebuilding but just adding additional storage to a RAID 5 initially configured with 3 drives. I already have files on the RAID drives but wish to add another without messing up this data.

Duncan
Steve Mann wrote on 12/10/2005, 3:00 PM
My guess is that it would not recognize the additional drives, and at worst, the controller would think the whole array is broken.
richard-courtney wrote on 12/10/2005, 4:21 PM
I checked our software (from 3ware not 3com) allows a drive to be
added to the array so you can expand storage. It will rebuild and
can be scheduled to start at a later time (offpeak). So, yes it will
be possible to add another drive up to the max number of ports
on your card.

Check your controller's manual for howto instructions.
gdstaples wrote on 12/10/2005, 5:13 PM
Much appreciated. The controller manual does not reference this but I can call their tech support to get an answer.

Man these things take forever to format the first time. Like 24 hours for a 1TB RAID 5.

Duncan