If a raid controller changes, are the drives still usable without re-formatting?

Question

I've been wanting to do a raid 1 setup in my home with a pair of sata drives. Someone told me that if the controller fails, you can't just get a new controller because you'll have to reformat the drives.

Or is that true only in some implementations? I was originally just looking at an onboard raid controller, or an entry level nas drvice like the intel SS4200-E, but If the hardware (controller) ever fails, will I be out of luck accessing the data if I can't get the exact same hardware to replace it?

Answer 1

Maybe, maybe not. That's *exactly* why I use software raid. I could care less about performance, in exchange for guaranteed compatibility. I know it's a religious issue, but that's a no-brainer in my world.

Answer 2

Typically yes the config is per controller type. So if you have a failed controller and can't replace it with the equivelant you'll probably be SOL.

As long as it's the same kind though, I've never seen one which wasn't able to import the config from the drives. This is usually stored on each drive.

Answer 3

If you're using RAID-1, then the controller is usually not relevant. In fact, you SHOULD be able to take a drive from a RAID-1 pair, and plug it into a normal controller and it should work. I've done it in the past.

The only thing you will need to be careful of is which controller you replace it with. Some controllers (the ones in our Dell blades, for example) will only make a RAID-1 array by destroying both disks. Some controllers will let you choose a Source, or Primary disk will not be wiped when creating a RAID-1 array.

Answer 4

Or use the OS level RAID1 feature instead of a card - then the controller for the disks wont matter (and as we're talking RAID1, mostly any OS will be able to boot from it for the reasons Farseeker put through as well).

Answer 5

It would depend on how the specific controller implemented the array. If it stores all the config in the controller and does no format abstraction, it may be able to be bypassed. You could test for that by setting up the initial array and then pulling one of the drives and connecting it to a regular disk controller.

If the array can be moved between systems ("use disk config or use controller config" type prompt) or can accept non-identical drives in the array, there is likely some abstraction happening. You'd likely need a controller which uses the same format (which in practical terms means an identical card) if the existing one failed. Or you could just decide that on controller failure you'd fall back to the most recent backup.

Answer 6

If you know the parameters the RAID container used, and it was something simple like RAID 0, 1, 3, or 5, then you can perhaps get lucky if you know someone who can code.

I had a CMD raid controller fail, and after a bit of (easy) sniffing around on the drives, I found that each drive had the RAID set configuration stored in the first few blocks. Skipping that, and writing a simple program to read from each drive in the correct order (including RAID 5's rotated parity) I managed to recover all the data.

Answer 7

Based on my home experience - do not spend your time with anything below RAID 5 :) Troubles of migration or crash recovery are much higher than performance gained.