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Old 12-06-2008, 10:01 PM   #1
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data recovery from raid5 drives

I was recently charged with increasing the storage of a linux file server. Seemed simple enough at first, I figured it could be done in an evening without too much effort. Then I found out that the megaraid controller wasn't recognized by any bootable CD I had. The particular raid controller is an American Megatrends Megaraid version 02.
In the end, with a current debian testing image, I did get the system running with three new drives in a raid5 array, and I did do it in the evening I had alloted for it. But when I went back to install the machine the next day, I discovered I had not copied all the files I needed to before I took the old drives out, and the machine was back in production, so I couldn't exactly shut it down and put the old drives in. Besides, even if I had done that, I am not sure that the megaraid controller would see the old raided drives, now that the controller has been reconfigured with the new drives.
I figured I could use software raid to recreate the array, and after some poking around, I did find a few posts on people who had used that trick for a raid0 and raid1 config, and one who had used his skills as a java programmer in conjunction with gnu/linux to recover a raid5 of 5 disks.
I have the drives in a machine and have booted up with the gparted live cd, but nothing really seems to be functioning the way I had hoped. /dev/hda-b-c are the three drives, /dev/hdd is the cd. querying the drives with madam -Q tells me /dev/hd* is not an md array, and mdadm --examine tells me there is no md superblock detected on any disc, or any partition thereof. parted tells me /dev/hda and /dev/hdb have paritions outside of the disk, and /dev/hdc is an unrecognized disc label. ls /dev/hd* seems to indicate there are 4 partitions on hda and hdb, but no partitions on hdc.
I have perused the man page for mdadm, and do not see any other options for recovering the array this way.
So now, while I am doing this post, I am also looking for documentation on the particular raid controller to see if I can put the drives back in the original machine without danger of losing the data. But I am hoping somebody has some other ideas for me to try using mdadm or some other piece of software available to the linux world...
All comments appreciated...
Old 12-07-2008, 01:10 AM   #2
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I have a fair bit of experience with 3ware, software, and other RAIDs. One important distinction is hardware vs software RAID. The mdadm utility may only be used for management/recovery of software RAIDs. Almost all hardware RAID controllers use their own proprietary formats for the drives, which will make it difficult for recovery without re-connecting it to the hardware controller.

Yes, recovering a RAID1 from a hardware controller should be pretty easy. Recovering a RAID5 will be more difficult, because you have to reverse engineer the chunk sizes and rotating parity.

However, you should be able to safely re-connect the old drives to the RAID controller. They are designed to allow this.
Old 12-07-2008, 02:58 PM   #3
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thank you for your reply. Looks like reconnecting is the best I will get, so I will try that...


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