Can a mirrored (RAID-1) disk be plugged into another system to be read?

Question

If I have some disks in a RAID-1 configuration, can I just take out one of them and plug it into a different system to be read?

I mean treating it on the target system just like an ordinary disk, regardless of any controller/driver support and without doing any rebuilding.

The idea is that if somehow my array (of 2 disks) degrade, I don't have to get another disk with the same capacity (getting harder nowadays as time passes) and hopefully even without access to the original system. Or maybe instead of the array dying, it's the controller/motherboard that does.

Of course, I know that if it is possible, than I may not be able to simple put them back together again as the data may be out of synch, but it's a different case. :)

Answer 1

regardless of any controller/driver

Disregarding RAID implementation? Then the answer should generally be no: you can not assume that all hardware controllers treat disks in such a transparent way.

However, in the case of software raid in Linux (md+raid1) then yes, there's no disk header or secret block-level optimization going on there.

In the case of Disk Mirroring in Windows, it involves the disk having been initialized as "Dynamic" and, well, should just work, given that the system that reads it can understand the dynamic volumes - in other word it will most likely only be accessible from another system running Windows.

In the end; you can try connecting the disk regardless of controller. If it works, it works. No controller will damage the data on the disk as long as you don't tell it to - i.e. as long as you don't execute an operation such as "initialize" or anything.

Answer 2

Only if things are the same, ie same raid controller, or the same kind of software raid supported (IE, I would expect than any software raid created today would be supported in the future, but the deprecated stuff may well go away at some point).

Switching between hardware raid can be finicky.

Answer 3

You won't necessarily be able to access the disk as just a normal disk, but you should be able to instruct you local system to access it as part of a degraded RAID-1 array and read the data just fine.

If you need to do this and are using hardware RAID, you would need the same kind of card, or in case of software RAID you would need the same software.

Note that some implementations make it look like the disk is a normal disk with a normal disk header, but I would be very wary of just using it as-is; the RAID information might conceivably be tucked in there somewhere and ruin your day.

Answer 4

This is not guaranteed to work, but in many cases it will work. One specific example, I took one hard drive from a Raid-1 array created by an ICH9R chipset, plugged it into a system with a SB600 chipset, and was able to successfully boot off of it.