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Two years ago I bought a WDC MyBookWorld II NAS which is using Linux software RAID internally. I thought it used RAID1 but it turned out that in my case it used linear mode. I was stupid enough not to pay much attention to this. One of the drives is dead now(it works very unstable, may work for a while and then just go down for no reason).

I really want to restore anything from the linear raid partition of the working drive, is it possible at all?


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Get a new drive and do a block level copy to the new drive first. With dd_rescue you should be able to pull most of the data out if it.

After that, start your array as normal, with the old working and new drives present.

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You mean to make a block copy of the defective drive or a working one? – pachanga Oct 5 '10 at 10:19
the defective one. Usually, even if you have read errors, the drive is able to read the sector once every few, few hundred tries. If dd_rescue will show that all reads succeeded, the block level copy will be usable with MD driver. You have to note though that some drives can lie about correct reads (read data with incorrect checksum and still pass it to cpu), but such situations are rather rare. Remember to use the log-file with dd_rescue! – Hubert Kario Oct 5 '10 at 15:38
There is a problem, the defective drive can work reliably only for a few minutes, then it just dies.... – pachanga Oct 5 '10 at 16:33
If the drive works for few minutes before dying it's enough to transfer some data off it, dd_rescue remembers which parts it read and starts with unreadable on next try (that's the log file I mentioned). As for recovering from the first one, it may be rather hard, especially if the superblock lies partially on the defective disk. – Hubert Kario Oct 5 '10 at 16:43
You could try using a USB bridge (they can be bough for close to nothing), this way you should be able to a). keep the system running after disk crash b). reboot the drive without rebooting th PC – Hubert Kario Oct 5 '10 at 21:24

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