RAID 5 rebuild question

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telecentricity
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RAID 5 rebuild question

Postby telecentricity » Sat Aug 09, 2008 11:14 am

I have a question about rebuilding a 3 disk RAID 5 system running
Intel Matrix Storage Manager ver 6.1 on an Intel DG965OT board.

Yesterday I moved the entire system (motherboard, CPU and disks) to a
new box that has more room. I reconnected the SATA cables in the same
order I took them off. I did not make any hardware changes except
that I removed some jumpers from my Seagate 7200.10 drives to remove
the 1.5G/s limit.

When I did the POST, the Matrix Storage Manager came up as failed RAID
volume and only 2 of the 3 drives showed up. I had forgotten to plug
in the last drive.

I reconnected the final drive. Now all three drives show up green but
the RAID volume is still red "failed". I have an option to rebuild
the array, but I am afraid that I will erase my data on my existing 3
disks.

Does rebuild automatically erase everything?

Did I do something wrong by removing the jumpers - should I replace
them?

Any help would be greatly appreciated - I surfed the forum but did not
find an answer.

Kind regards,

Telecentricity

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Re: RAID 5 rebuild question

Postby DMB2000uk » Sat Aug 09, 2008 11:46 am

Raid 5 is the one with the built in parity drive?

If so and it thinks one of the drives are bad it will just rebuild the missing data (or the parity drive) from the two 'working' drives. Your data should be fine.

Dan

PS. Try resetting the CMOS and entering all the BIOS settings again to see if it picks up all three drives properly again.
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telecentricity
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Re: RAID 5 rebuild question

Postby telecentricity » Sat Aug 09, 2008 3:26 pm

Dan,
Thanks very much for your reply. I did a CMOS reset by pulling the battery and waiting 10 seconds. The Intel Matrix Storage Manager now comes up with three green drives and the status of the RAID 5 volume is "rebuild". OBTW the volume states that it is bootable. So if I allow it to rebuild will it in fact still contain all of my data, or will the rebuild process result in a clean, formatted, blank disk?
I ask the question because Intel support told me that if the volume is degraded (i.e. lost only 1 disk), it will rebuild with data, but if it was listed as "failed", as in my case, rebuild is impossible. This doesn't really make sense because all three of my original drives are in good working order.
Thanks again,
Gary

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Re: RAID 5 rebuild question

Postby Zertz » Sat Aug 09, 2008 3:48 pm

Isn't that the point of RAID5? Parity is distributed amongst the 3 drives, so if one fails you can replace it and rebuild without a problem.

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Re: RAID 5 rebuild question

Postby DMB2000uk » Sat Aug 09, 2008 5:03 pm

Zertz wrote:Isn't that the point of RAID5? Parity is distributed amongst the 3 drives, so if one fails you can replace it and rebuild without a problem.

From the explanation from the quoted Intel tech that seems to be the difference between degraded and failed.

After the further clarification from the intel tech's comments, I'm now not so confident that rebuild is going to keep your data.

If it is still bootable, is there no option to boot into it?

Dan
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telecentricity
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Re: RAID 5 rebuild question

Postby telecentricity » Sat Aug 09, 2008 5:48 pm

I am getting mixed messages whether a rebuild from a failed RAID volume will restore my data or not. The tech guy from the computer store where I bought my components told me the data was definitely gone (?!).
Right now I am doing a clean install of Windows XP and the Intel RAID drivers onto a spare disk. I plan to boot from this disk and then access Intel Matrix Storage Manager from within Windows to see if it gives me any more options to rebuild the degraded array.
The Intel website is no help - they keep saying failed RAID volume = lost data, no exceptions.
I am still curious why my IMSM gives me a rebuild and a "bootable yes" flag - looks like I can rebuild it without a problem. Remember that none of my hard drives have failed.
Well, this all serves me right - I am a RAID dilettante who got in over my head.
Any further thoughts are greatly appreciated.
Gary

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Re: RAID 5 rebuild question

Postby telecentricity » Sun Aug 10, 2008 8:09 am

Problem Solved,
I ended up ignoring Intel tech support and I used common sense instead. I let the POST run and the computer booted to windows. I let the array rebuild overnight and today it works fine.
I would think that if Intel Matrix Storage Manager says that the RAID volume is bootable, then your data must still be intact, regardless if the volume was listed as "failed" rather than "degraded". This contradicts the Intel manual and their website.
I did stumble across a program called RAID Reconstructor that promised to restore my array. Some other forums recommended it. In the end I did not need it but I will remember it for the future.
Thank you for your time & advice,
Sincerely,
Gary

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Re: RAID 5 rebuild question

Postby DMB2000uk » Sun Aug 10, 2008 10:09 am

Glad you were able to get everything fixed and kept your data.

Make sure you don't boot without one of the drives plugged in in the future!

Dan
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Re: RAID 5 rebuild question

Postby Zertz » Sun Aug 10, 2008 9:35 pm

From wiki:

RAID 5: Striped set with distributed parity. Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive.

(Consider your unplugged drive as if it was a drive failure)

If rebuilding wouldn't have worked... then you might as well go RAID0 because the whole point of 5 vs 0 is security

Anyways, nice to see you got everything back up and running

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Re: RAID 5 rebuild question

Postby BONZAII42 » Wed Feb 27, 2013 11:06 am

My problem is only one hard drive went bad. I replaced with identical drive and now it shows all 3 HD's in green, says they are member disks, and under the status it says "rebuild" but it won't boot into server 2008 OS. At bottom in yellow it says "volumes with "rebuild" status will be rebuilt within the operating system" - but it won't boot into system.

Using RAID5 intel board matrix storage manager ROM v8.6.0.1007 also shows ICH10R/DO

HELP!!!

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Re: RAID 5 rebuild question

Postby egloeckle » Thu Mar 21, 2013 10:12 am

Wow, had this been posted in storage I would have caught it sooner and saved you some headache. The following pertains to RAID5 (and in some cases RAID in general).


Degraded: single drive failure, the array *should* still boot and run and all however it is running that 'missing' drive off parity. Replace the drive immediately.
Failed: Multiple drive failure. In RAID 5 this means 2 drive failure, in raid 6, it means 3.

Rebuild/resync: This is necessary in 2 cases. 1) bad drive has been replaced. 2) array is booted without one drive in the array for some reason causing the drive to be 'out of sync'. This rebuilds the new/out of sync drive using parity data. You *should* not lose any data doing this process, however be aware that you can still lose data. I have a post on how/why you can lose data in raid5 somewhere though I cant seem to find it right now, if you really care, let me know and ill repost/create that info here.

Hot spares take care of most of this automatically, you still need to replace the bad drive, but it will become the new spare. Being that you dont have a hot spare, this is just here as reference.

In your situation the proper steps would have been (note this is pretty much the same process for a failed drive):

1. Upon discovering one drive was not plugged into the system the array went into degraded mode. Doesnt matter that you did not boot off the drive. The raid controller correctly detected the drive missing and flagged it. This is GOOD.
2. Shut off the machine immediately. Reconnect the missing drive.
3. Upon booting verify the controller picks up the previously missing drive.
4. When prompted, allow the array rebuild. The 'degraded' drive will be resync'd to the array. This can take many hours depending on the size and speed of the drive.
5. After the rebuild is complete, reboot the system. Ensure everything comes up as 'normal' dealing with the array.
6. Run an OS level disk check (chkdsk, fsck, etc)
7. Reboot one more time just to be sure.
8. Ensure that your backups are working properly. RAID is NOT a backup. :)


Edit: Just caught that this was a necro'd thread. The above is still valid info in case anyone runs into similar in the future. To the person who necro'd the thread, DONT DO THIS!


Edit 2: I just caught that your array was marked 'failed' in the intel controller and not degraded. The rebuild is still worth a shot, the Intel RAID controllers are typically not 'real' raid controllers though I dont know in this specific case. Typically on these types of controllers the 'RAID' is actually software controlled with a hardware component, though the software/driver is what actually handles the RAID not the actual controller itself. These controllers suck and you may as well not bother with anything over RAID 1 in this situation. I am guessing if the rebuild worked, that intel controller just uses some odd terminology or displays the data weird and was saying 'failed' for a single drive though made it appear like it was the entire array.

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Re: RAID 5 rebuild question

Postby egloeckle » Thu Mar 21, 2013 10:21 am

BONZAII42 wrote:My problem is only one hard drive went bad. I replaced with identical drive and now it shows all 3 HD's in green, says they are member disks, and under the status it says "rebuild" but it won't boot into server 2008 OS. At bottom in yellow it says "volumes with "rebuild" status will be rebuilt within the operating system" - but it won't boot into system.

Using RAID5 intel board matrix storage manager ROM v8.6.0.1007 also shows ICH10R/DO

HELP!!!


Dont hijack/necro threads and I wont post answers to 4 year old posts before I catch it. Start a new thread and maybe someone will help you out.


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