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Old 10-30-2008, 12:18 PM   #1
Registered: Oct 2007
Posts: 32

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Help Bring Partition Table Back from the Dead-Centos 5 (RHEL)


I need some advice. Here is what happened:

The set-up:

Two 4 port High Point 1740 SATA controllers. Each controller had four 250GB drives attached to it. Each controller was set-up as a separate RAID5 with one spare drive. In Centos 5 Linux, this created two drives in /dev, sda and sdb.

I needed a large storage space, without (as I thought) a high level of safety. So I partitioned the drives in parted and created sda1 and sdb1. I then used mdadm to create a RAID0 system across these two drives. The RAID device is called md0.

Everything worked fine. It was doing exactly what it was designed for, which was a large (1TB) temp storage space. Then people saw that it was a large storage space, so they started storing semi-critical data (images) there. They stored a lot of this data 300+ GB. Then we had a power surge. The power surge damaged the power supply. It wasn't damaged enough to just drop the motherboard or fry a drive, it acted slowly. It started with one drive on the second controller. It worked intermittently during one week (while I was on vacation). When I got back to work on the machine, another drive dropped, then another in quick succession.

So I replaced the power supply and hooked the drives back up. Two of the three dropped drives came back. One of the drives was completely dead. I was able to add a spare drive and use the High Point supplied GUI to rebuild the RAID5 array.

Here is where it stands: sda and sdb appear in /dev. That is good. sda1 appears in /dev. that is good. sdb1 does not appear in /dev. That is bad. Apparently, the partition table was dropped on the second array. When I run mdadm to rebuild, it tells me there is only one drive (sda1) in the array. When I run parted, it cannot find any partition information on sdb.

So here is where I am at. Does anybody know of a way to restore/rebuild this partition table? Are the tables identical in sda1 and sdb1? What I mean is, in a RAID0, are the tables written across the drives? Can I copy the table from sda1 to sdb? How do I do that?

Thanks in advance. And I already know, it was a stupid set-up, it was a frail system, etc., etc. But before you let me have it, take this into account: the power surge was caused by the owner of the company indiscriminately throwing circuit breakers Even better: he was throwing circuit breakers with an electrician because they were trying to determine how to run power down to the new data center.

Old 10-30-2008, 12:43 PM   #2
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Registered: Feb 2003
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You could try testdisk:

Steve Stites


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