I was handed a Seagate NAS with 4 HDDs set up as RAID5. One of the drives failed: won't spin up, clicks, etc. The other 3 drives are fine. They spin up, when connected via USB, the data on them is clearly visible with a hex viewer.

Seagate has instructions for restoring a failed RAID5, is calls for a new drive, among other things. The problem is that a crucial [ rebuild ] button is missing from the interface and Seagate has no further instructions except to call their data recovery service, which is $$$$$.

My question: is there software that can do the following:

(1) Rebuild the drive given 3 other drives connected via USB (I took the drives out of the NAS). (2) Mount the resulting software RAID5.

I have access to Mac OS, Windows, and if need be Linux machines. I'd prefer a solution with fewest question marks for safety of the entire array. Note: the files which the user seeks to recover aren't JPG, XLS, and the such. They are highly-specialized format not included in disk scanners. Which is why mounting the resulting software RAID is a requirement.

  • What model NAS and how large the disks? Data recovery from a RAID5 array outside the NAS is way outside "fewest question marks to safety" unless you can bitcopy thile disks and work off those. If you can establish the NAS is mdadm based, your chances are higher. – davidgo May 4 at 7:41

Most probably the NAS uses Linux so it should be easiest to restore the RAID with Linux. In addition it can be done perfectly safely.

After connecting a drive you can use dmsetup to create a virtual block device with a 1:1 mapping to that drive. But this device mapper device can be created read-only so that it cannot be damaged when you experiment with mdadm. If you can create a read-only RAID then you can use mdadm on the original drive block devices to create a regular, read-write RAID.

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