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Raid-1 is mirroring two disks (if I haven't messed up completely here :p). Does that mean that I could take one disk out and put it into another machine and it would work like a normal disk? Or does it still only work in the raid? I can understand that a Raid-0 of course only works as a whole. But with mirroring I am not so sure how it works...

Of course putting the mirrored disk back in the raid afterwards would be a bad idea, but just taking it out... how would that work? Does raid store any special data on a drive that is needed? or does the raid controller handle everything like that and the harddrives are just used like normal?

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I asked a question dealing with this issue you are describing too. See it here: serverfault.com/questions/61024/… –  7wp Sep 1 '09 at 22:56
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3 Answers

up vote 6 down vote accepted

Well, the REAL answer is that it depends on the RAID controller. There's Hardware RAID and there's 'Fake RAID' -- which is basically a ROM implementation of software RAID.

Fake Raid will always require the same controller, just as using a linux software raid will require the same operating system (and sometimes the same kernel module version).

Real hardware RAID will SOMETIMES mean that you can swap them between machines, but in some cases you will need to have the same or a similar RAID card. One case where I've seen this is with a RAID5 volume on a Dell PERC/3di card. I haven't ever tried it with RAID1, but I understand it's possible.

Does raid store any special data on a drive that is needed?

Usually, yes, it does.

or does the raid controller handle everything like that and the harddrives are just used like normal?

Sometimes this is true -- either independently from the data on the drive, or in concert with data on the drive. i.e. the drive may have metadata readable only to a certain class of controller that says it was part of a RAID1 pair, and other controllers will ignore that metadata.

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This depends entirely on the RAID used. It's entirely possible for different RAID cards and different RAID software implementations to have an on disk format that doesn't let you use a single disk by itself.

However, I know at least Linux's md software RAID does lay things out so you can use a single disk outside the RAID.

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Yes in most cases this is correct, you can use the disk in a another machine.

It isn't uncommon to use a disk from a mirror set to clone a machine.

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In most hardware implementations of RAID-1 that I have encountered, this will NOT work, unless you have the matching RAID controller in the new box. Software RAID-1 would seem likely to depend on the OS. –  geoffc Jun 11 '09 at 15:47
Very true it is dependent on the controller or raid software versions. As a side note, many of your built in SATA raids are software raids. –  Brettski Jun 12 '09 at 15:52
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