Change Raid controller & keep raid intact?

Posted on 2009-02-10
Last Modified: 2013-11-14
Hi All,

    I realize the actual answer is "it depends".  However I am looking for a general pattern.  What I am concerned about is creating a RAID array (1 or 5, etc.) and having trouble with a faulty controller down the line.  I can pick up a promise raid card or even use a smart-array on an HP/Compaq.

   What I'm wondering is what happens when you go to replace a component like this?  Do you replace the card, reconfigure a raid with dummy drives?  Can you swap an existing raid "pair" (for example) and pull the drives and plant them onto another server?  Some have said that the raid info is kept on either the controller, the drives, or both.  I don't have a lot of equipment to experiment with, but I am looking for, again, patterns.  I'm happy to clarify if need be.

Question by:Attenuation
    LVL 31

    Accepted Solution

    With lower end cards like Promise, I think all information is kept on the drives. If you switch the controller, the data is gone, even if you reconfigure it with "dummy drives". On higher end cards like Dell's PERC controller or the HP Smart Array controller keep data on both the drives and controller. If the controller fails, and is replaced, when you reboot the server it comes up and says something to the effect of a configuration mis-match. You then have a choice of using the configuration on the drives or the controller. This is the best option. On a Dell, I have successfully moved a 6 disk drive, RAID 5 to a different, identical model server (the drives must be put back in the same order), and successfully brought the server up and accessed the data.
    LVL 33

    Assisted Solution

    My 'rule of thumb' is:
    - same brand controller, chipset, revision# --- really good chance of moving it intact
    - same brand, chipset, different revision# -- almost as good a chance
    - different brand, same chipset, revision# --- decent chance (there's always the risk the different brand did something)
    - same/different brand, different chipset --- not so much. The more the difference, the less likely. And it's a fast curve.

    I have taken a raid1 off a dead onboard controlled, and put it on a PCI controller with the SAME chipset, and it fired right up like nothing happened.
    LVL 55

    Assisted Solution

    Smart Array doesn't store any configuration on the controller AFAIK, it's all on the RIS metadata on the disks. Smart Array RIS is consistent through the range so you can swap any Smart Array with any other within reason. Best to upgrade to the latest firmware first. The RIS metadata is proprietory so you cannot replace a Smart Array with someone elses make or vice-versa.

    Author Closing Comment

    Thanks all!  Thanks to rbarnhardt for the global insight and to the others for additional follow-up.  I very much appreciate it.
    LVL 33

    Expert Comment

    Thank you much.   : )

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