ArticlesI need a guide to the way RAID controllers work.
I don’t need any of the hundreds of web-sites that tell me the basics: “RAID stands for Redundant Array of Inexpensive Disks. RAID comes in several levels. RAID is good.”
I don’t need the manual that comes with the RAID controller that tell me “The RAID Set menu lets you add and delete RAID Sets. To delete a RAID Set, select Delete RAID Set menu item.”
I need a guide that explains how the RAID format on the disk differs from a regular disk, so I understand the consequences of my actions – so I can know when it is appropriate to delete a RAID Set, and whether one of those “inexpensive” disks can be successfully moved between disk controllers.
My search still hasn’t found that. Peter Norton, where are you when I need you? Are these sorts of manuals a lost art?
Sigh.
Comment by Sunny Kalsi on October 8, 2005
it should be completely determined by the level. If mirroring, for example, both disks should be identical and work on another PC with no RAID. For striping, you need a raid controller that supports the same level of striping. And you need to know which disk is #1, #2, #3. That really ought to be all. There’s no “metadata” associated with RAID, so I don’t see how anyone could have any problems.
Comment by Julian on October 8, 2005
Clearly I am in no position to claim to be an expert, but, given I wasted many hours when I deleted some of the metadata associated with a mirrored RAID disk, I guess I can confidently contradict you.
To start with, when a RAID controller boots up how does it know whether its two disks are supposed to be mirrored, without some metadata being stored somewhere? Where is that stored? I can confirm that my original suspicion (stored in NVRAM on the controller) was false.
The scenario I was in:
I had two mirrored disks.
Disk #1 got corrupted (Motherboard died at the same time => Power surge?)
Both disks got moved to a different (non-RAID) controller. Disk #2 worked fine (no data loss, yay for mirroring!), but Disk #1 was still corrupted.
Disk #1 got reformatted, and tested okay.
Disk #2 was copied over Disk #1 (file-level copy, not mirrored).
Both disks were moved to the original controller, which reported errors in the RAID-set. (What RAID set? They were still separate disks!)
I figured they weren’t really in a RAID configuration, so I deleted the RAID set. That corrupted both disks, and they wouldn’t work in either controller.
Comment by Sunny Kalsi on October 11, 2005
It seems you’re right about the metadata. That’s what allows software raid to work. File level copying wouldn’t work, because RAID works at the block level, so the mirror would’ve been incorrect.
I don’t understand what you mean by “Deleting the RAID set”. Did you remove the metadata, or did you remove the partition? Clearly, removing the partition would’ve killed both drives.
It seems that there’s a bunch of formats.
http://www.die.net/doc/linux/man/man8/dmraid.8.html
If it was me, I’d put the drive in the non-raid controller and try looking at it with fdisk. If the drive is physically fine as you say, it might turn up something interesting.
Comment by Julian on October 20, 2005
I thought I was removing the metadata. The result was the partition(s) were gone.
I didn’t do exactly this – but I did the equivalent, using a different recovery tool. I recovered all of my data.
Comment by Jay de Silva on May 23, 2007
I don’t know whether the comments above have answered the original question, as I have a related one, and its not answered. I suspected that my motherboard HDD controller is faulty as it corrupted one of my disks. The only IDE/PCI hdd controller I could find was a RAID controller, and this has worked perfectly, but takes an inordinately long time to shutdown Windows. I suspect that it is doing some background mirroring, which I don’t want (I did not configure the controller when I installed it, and it probably mirrors by default).
When booting up, it gives an option (F3) to enter the RAID utility, which lists the disk(s) and permits a RAID set to be removed.
My qusetion is, if I Remove the RAID set, will it stop mirroring (which is what I want), and let me use the HDD without any RAID functionality, or will it corrupt everything?
Thanks