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This is a really simple question, and the answer is probably encoded in various wikipedia articles, however my question is reasonably specific, and I need a bulletproof answer! I'm not sure if my question pertains to hardware RAID in general, or to the specific RAID controller I'm working on. Either way it is the Dell SAS 6/iR (this is an LSI sas1068e chipset).

I simply want to:

  1. remove a set of striped (RAID 0) disks from this RAID controller in a server
  2. put in another set of disks, and create a RAID 1 array (or create a new 'virtual disk', as they call it in the SAS 6/iR manual)
  3. Do stuff with the new RAID 1 array
  4. Have the option of putting back the old set of disks (the RAID 0 striped ones)

I am quite sure this is possible, but I need some form of reliable, evidence-based answer as it's for a client of mine, and I need to migrate their data safely.

The question: can I actually do the above? Does the RAID configuration get stored on the disks themselves, or in the hardware controller? Is any data stored in the hardware controller?

If there is any chance I cannot completely restore operation of the first set of disks I removed, then I need to know about it!

The manual alludes to the answer to this question (see page 45 of this document), and talks about activating an array of disks.

I just need someone to confirm I can definitely do the above.

See, simple question, right? :)

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2 Answers

up vote 0 down vote accepted

I can tell you out of experience that yes this works. The way Raid works is that the meta-data is stored on the disk itself, this allows for the disks to be set up every single time the computer is powered on, and why the controller must boot itself, check the drives, and then set up the array. This is also how information is stored on parity disks and can be retrieved when(in set ups such as RAID 5) one of the hard disks dies.

In fact, if you were to take those drives and set them up in a different server/motherboard with the same controller, your information would be intact. It all depends on the controller, because of the way in which the information is stored and the way in which the company approaches data-correction and data-recovery at a bit-level.

Parity files are wondrous things. I hope this has answered your question.

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Thanks very much. This made me feel a lot more secure. I ended up not requiring to swap the old set back in. But I couldn't have done it without knowing that for sure! –  hazymat Oct 7 '12 at 15:13
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For an absolute bullet proof answer: Phone the manufacturer (Dell).

As for a general answer: Most (and all modern) hardware RAID cards I have worked with store their information on the drives, not in some nvram on the controller. So yes, it should work.

But until you encounter someone who did precisely what you asked with the same controller, same disks configuration etc. etc. you will not get a bullet proof answer. For that you really need to ask Dell.

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Could whoever down voted this please tell me why? –  Hennes Oct 7 '12 at 2:26
    
It wasn't me to vote it down. I actually found this response helpful. I tried to vote it back up again but I don't have enough reputation to vote it up... –  hazymat Oct 7 '12 at 15:15
    
Wasn't me, must be some silly troll –  AlanTuring Oct 7 '12 at 16:08
    
What bothered me is my failure to understand why. (Personally I thought my response was a bit short. And I might have triggered on the d I need a bulletproof answer!. Even though I am 95+ % sure that it would just work. Not 100% though. Which is not bullet proof. I would risk it with my own data though. –  Hennes Oct 7 '12 at 16:39
    
i think it probably has something to do with something like, you're providing a suggestion but not a concrete answer which is what the OP asked for. Either that or it was just a troll, i wouldn't pay too much attention to it. –  AlanTuring Oct 7 '12 at 17:50
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