Comments on: RAID is of the Lost Art http://www.somethinkodd.com/oddthinking/2005/10/03/raid-is-of-the-lost-art/ A blog for odd things and odd thoughts. Wed, 08 Sep 2010 05:22:51 +0000 hourly 1 http://wordpress.org/?v=3.0.1 By: Jay de Silva http://www.somethinkodd.com/oddthinking/2005/10/03/raid-is-of-the-lost-art/comment-page-1/#comment-40774 Jay de Silva Tue, 22 May 2007 22:36:35 +0000 http://www.somethinkodd.com/oddthinking/?p=93#comment-40774 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 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

]]> By: OddThinking » Version Number Challenge http://www.somethinkodd.com/oddthinking/2005/10/03/raid-is-of-the-lost-art/comment-page-1/#comment-1197 OddThinking » Version Number Challenge Thu, 20 Oct 2005 12:43:25 +0000 http://www.somethinkodd.com/oddthinking/?p=93#comment-1197 <!-- UnMarkedDown_2_01132522737--><p>[...] Here’s a little challenge for the software developers. It arose as I considered the meta-data in a RAID configuration, but it has wider applicability, so I will generalise a little. It is probably a solved problem in Computer Science, but I’ve not heard of it before, so I will happily reinvent this wheel. I do not have a good solution yet, but it seemed an interesting puzzle. [...]</p>

[...] Here’s a little challenge for the software developers. It arose as I considered the meta-data in a RAID configuration, but it has wider applicability, so I will generalise a little. It is probably a solved problem in Computer Science, but I’ve not heard of it before, so I will happily reinvent this wheel. I do not have a good solution yet, but it seemed an interesting puzzle. [...]

]]> By: Julian http://www.somethinkodd.com/oddthinking/2005/10/03/raid-is-of-the-lost-art/comment-page-1/#comment-1136 Julian Wed, 19 Oct 2005 14:54:42 +0000 http://www.somethinkodd.com/oddthinking/?p=93#comment-1136 <!-- UnMarkedDown_2_01132522737--><blockquote>Did you remove the metadata, or did you remove the partition?</blockquote> <p>I <em>thought</em> I was removing the metadata. The result was the partition(s) were gone.</p> <blockquote>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.</blockquote> <p>I didn't do exactly this - but I did the equivalent, using a different recovery tool. I recovered all of my data.</p>
Did you remove the metadata, or did you remove the partition?

I thought I was removing the metadata. The result was the partition(s) were gone.

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.

I didn’t do exactly this – but I did the equivalent, using a different recovery tool. I recovered all of my data.

]]> By: Sunny Kalsi http://www.somethinkodd.com/oddthinking/2005/10/03/raid-is-of-the-lost-art/comment-page-1/#comment-880 Sunny Kalsi Tue, 11 Oct 2005 00:05:57 +0000 http://www.somethinkodd.com/oddthinking/?p=93#comment-880 <!-- UnMarkedDown_2_01132522722--><p>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.</p> <p>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.</p> <p>It seems that there's a bunch of formats. http://www.die.net/doc/linux/man/man8/dmraid.8.html</p> <p>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.</p>

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.

]]> By: Julian http://www.somethinkodd.com/oddthinking/2005/10/03/raid-is-of-the-lost-art/comment-page-1/#comment-864 Julian Sat, 08 Oct 2005 09:56:52 +0000 http://www.somethinkodd.com/oddthinking/?p=93#comment-864 <!-- UnMarkedDown_2_01132522720--><p>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.</p> <p>To start with, when a RAID controller boots up how does it know whether its two disks are <em>supposed</em> 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.</p> <p>The scenario I was in: </p> <ol> <li><p>I had two mirrored disks. </p></li> <li><p>Disk #1 got corrupted (Motherboard died at the same time => Power surge?)</p></li> <li><p>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.</p></li> <li><p>Disk #1 got reformatted, and tested okay. </p></li> <li><p>Disk #2 was copied over Disk #1 (file-level copy, not mirrored). </p></li> <li><p>Both disks were moved to the original controller, which reported errors in the RAID-set. (What RAID set? They were still separate disks!) </p></li> <li><p>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.</p></li> </ol>

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:

  1. I had two mirrored disks.

  2. Disk #1 got corrupted (Motherboard died at the same time => Power surge?)

  3. 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.

  4. Disk #1 got reformatted, and tested okay.

  5. Disk #2 was copied over Disk #1 (file-level copy, not mirrored).

  6. Both disks were moved to the original controller, which reported errors in the RAID-set. (What RAID set? They were still separate disks!)

  7. 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.

]]> By: Sunny Kalsi http://www.somethinkodd.com/oddthinking/2005/10/03/raid-is-of-the-lost-art/comment-page-1/#comment-863 Sunny Kalsi Sat, 08 Oct 2005 06:51:35 +0000 http://www.somethinkodd.com/oddthinking/?p=93#comment-863 <!-- UnMarkedDown_2_01132522720--><p>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.</p>

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.

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