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Is there a way to replace RAID card (RAID 5) by software RAID?

Posted on 2011-09-05
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Last Modified: 2013-12-02
Hi there,

We got a Network Attach Storage (NAS) server, which has RAID 1 for OS and RAID 5 for storage using a RAID card (hardware RAID).  Unfortunately the RAID card went bad.  I wonder if it is possible to use software RAID to bring back that RAID 5?

All opinions are welcome.  Thanks.

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Question by:asugri
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Ara- earned 400 total points
ID: 36486601
In my oppinion Software RAID isn't really a great idea. I would replace the RAID card.

You could probably set up the disks in RAID 5 with Software RAID, but are you thinking for recovery or just to replace the disk? You should have an external backup anyway..
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by:rindi
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Most NAS have a legacy OS which is stripped down to the bare minimum where you don't have many configuration options, so it is unlikely you can change the RAID configuration without data loss. Get another identical NAS and put the current array into the new NAS and you should be able to access the data, but make sure with the manufacturer first...
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by:klodefactor
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Yes it's possible, but risky.  And remember that it's possible the RAID card scrambled things a bit as it died, so you may need to run data recovery regardless.

As rindi says, getting an identical RAID card is probably safest.  However even that can be risky depending on whether the fir supports importing an existing RAID set.

If you absolutely need to avoid data loss, your first step should be to take a byte-for-byte copy of the hard disks.  That way you can start over again if you make a mistake.  You can copy drive-to-drive to a new set of disks, or as disk images.  Acronis, Ghost, and other disk imaging products support doing this, or use Linux (or other *NIX) if you're conversant.

Now, on to the work...
First conversion step is to learn where your RAID controller stores configuration data: in cylinder 0, at the end of the drive, or something more complicated.  Some RAID cards use one or more cylinders for configuration data, but hide them from the OS.  So if you have a 1000-cylinder drive, and the controller uses one for its configuration data, the BIOS sees a 990-cylinder drive.  If your controller uses that method, and the RAID configuration is at the start of the drive, your recovery just got more complicated.  I'll ignore that case for now but let us know if that's in fact what you have.

Second conversion step is to determine which drive is which: which one was the first drive in the RAID, the second, etc.

Third conversion step is to determine the RAID stripe size.

Fourth conversion step is to determine the parity block order used by the RAID card.  For example, assuming you have three drives, does the parity block move to the right:
data1    data2    parity
parity    data1    data2
data 1    parity    data2
or to the left:
data1    data2    parity
data1    parity    data2
parity    data1    data2
That should be enough information to be able to use the RAID set.  Now all that's left is confirming that the partitions are defined correctly, that the filesystems aren't corrupted, and then rescuing the data onto a new hardware RAID.

--klodefactor
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by:klodefactor
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Argh.  "fir supports importing" should be "firmware supports importing".

And it should be a "999-cylinder drive", not 990 cylinders.

--klodefactor
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by:McRonis
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It is not recommended to do that, not sure if it's possible.
Each RAID card brand have it's own "logic" , in few words:
If you have RAID5 with LSI raid card, you can't use those HDD in Areca controller, because Areca controller has other hardware, and your HDD wont work as RAID5 inside that controller. You will need to destroy old raid massive and make new one. The same works with software raid.
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by:klodefactor
klodefactor earned 800 total points
ID: 36503221
Of course it's not recommended, but it is possible.  Due to the complexity and risk (and thus the need to create a byte-for-byte copy before starting), this method is not suitable for normal operation.  Sometimes though, it's the only way to recover your data.

BTW if you prefer prefer a simpler approach, you could purchase recovery software that supports a RAID source, such as R-Studio (http://www.r-studio.com/).

One last thing: before connecting the drives to an MS Windows system for recovery, ensure you disable Windows automount (and possible re-signature) of hard drives using diskpart:
automount disable
automount scrub
--klodefactor
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