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

This means, on the target system, treating the disk from the RAID array just like an ordinary disk, regardless of any controller/driver support and without doing any rebuilding.

The idea is that if my array (of 2 disks) degrades, I can plug it into a different system and don't have to get another disk of the same capacity (which gets harder as time passes) and (hopefully) even without access to the original system, in the event that the controller or motherboard goes bad instead of one of the disks.

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Is this software or hardware raid? –  Teddy Dec 16 '09 at 5:41
    
The question is actually about the general case regardless of the actual implementation. My system is Intel ICH10R, though. –  RichN Dec 16 '09 at 6:54
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I understand that your question in a "general case" but there is no general answer. It depends on if it is a software implementation or hardware one and how it is implemented. –  MDMarra Dec 16 '09 at 16:29
    
For what it's worth: I unplugged one drive from an Intel ICH8R RAID-1 mirror and hooked it up to another PC with an external eSATA enclosure. Windows 7 on that second PC mounted the partitions found on that drive. Though, might have been helped by the ICH9R chip on that motherboard? –  Chris W. Rea Sep 5 '10 at 15:18

4 Answers 4

up vote 3 down vote accepted

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.

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OK, so the general answer is no. Btw, you noticed that I'm only talking about RAID-1 and not those with parity checks. I don't have another system handy so I can't test plugging into another one, however just now I realized that I could put my HD in a USB enclosure and see if I can access it. Apparently it works, but of course it only proves that it works for this controller and not in general case. –  RichN Dec 16 '09 at 14:37

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.

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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.

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But the new system would likely not know that it was part of an array, right? Otherwise it would mean that the RAID information is indeed tucked somewhere. –  RichN Dec 16 '09 at 14:29
    
@RichN: My point is that you would need to instruct the new system that the disk is indeed part of a RAID, otherwise bad things might conceivably happen. –  Teddy Dec 16 '09 at 22:55

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.

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