NAS RAID 6 Recovery

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AmeedMv

AmeedMv

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I have a Zyxel NAS540 setup in RAID 6 config. But 2 of the drives are showing as failed. I have looked at forums and a bunch of them say in a RAID 6 config it is able to recover the data if only 2 of the drives are failed. If so, is there anymore information I could get about the recovery process?
Also any information you require to answer this question are welcome..

Thanks.
 
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USAFRet
This is where the standard mantra of "RAID is not a backup" applies.

You have two things here:
Your data
The RAID array.

Your data should ALSO exist in a backup. Given that, all you need to do is recover/rebuild the RAID array with new drives.
Then copy the data back in.

2 dead drives in a RAID 6 is, in theory, able to survive loss of 2 drives.
What happened when you slotted in a new drive to replace one of the dead ones? And then a second?
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S Haran

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Yes a RAID6 should be recoverable with two drives missing. Zyxel operates using Linux Software RAID aka mdadm so recovery may be as easy as connecting the drives to a desktop computer and boot a Linux distro like Ubuntu.

Or you can try RAID recovery software like R-Studio or UFSexplorer.

Before proceeding you should check the SMART health status of each RAID member drive with a tool like CrystalDiskInfo. It is possible the RAID member drives are starting to fail. And also consider making clone images of each drive and performing recovery work from the images.

I prefer the Linux method of RAID/NAS recovery. If you get stuck or need help I am happy to assist.
 
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AmeedMv

AmeedMv

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Thats a start, although I would like to know how to get started on the process. I have intermediate IT knowledge but not much about RAIDs or NAS devices or Linux or Ubuntu. So I would be glad to know each process I have to undergo step by step. Also if I have to check the health status should I proceed by using a HDD dock and separately checking the health of the disks, same goes for the cloning of the drives, should I clone them each one by removing them from the NAS device?

And someone has said that it is possible to swap the failed HDDs and replace them with new HDDs and it would be possible to get back the data without any other method. (Although I think this is highly unlikely I had to ask since about 16 terabytes of data is at risk)

Here is an excerpt from an FAQ on www.sos-raid-recovery.com
"You should change the defective drive as soon as possible. Normally, the RAID controller will integrate the new HDD and recreate the data, so your RAID system will be completely secured again. This operation may last a few hours."
Can you please shed some light on this as well?

I hear it is quite complex repairing or rebuilding a RAID. Particularly the terms "parity" and "order of drives" comes up in forums, which leads for me to become a little hesitant on the recovery by myself. I would be glad to hear a step by step process if that is not too much. Thank you.
 
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S Haran

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Yes you would need to remove the drives from the NAS enclosure and connect them to SATA ports on a desktop PC.

If you replaced each failing drive at the time of failure while the RAID6 is still functioning in degraded mode then the RAID6 would rebuild itself. But at this point replacing drives is not going to help.

Yes you need to know the drive order, parity direction, chunk size, and drive offset if any. This info can be collected from the RAID6 meta data stored on each drive.

I've worked on hundreds of remote RAID recovery cases and sometimes it can be a rather complex task. The most difficult recovery cases occur after an end users failed DIY recovery attempts. So it is wise to tread carefully as it is possible to make a mistake that renders your data unrecoverable .

Creating drive clone images reduces the risk but even the cloning process itself can cause data loss if done improperly.
 
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USAFRet

USAFRet

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This is where the standard mantra of "RAID is not a backup" applies.

You have two things here:
Your data
The RAID array.

Your data should ALSO exist in a backup. Given that, all you need to do is recover/rebuild the RAID array with new drives.
Then copy the data back in.

2 dead drives in a RAID 6 is, in theory, able to survive loss of 2 drives.
What happened when you slotted in a new drive to replace one of the dead ones? And then a second?
 
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Solution
USAFRet

USAFRet

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My NAS box is a 4 x 4TB RAID 5. It WILL survive the loss of a single drive.
And I've actually tested this, to verify in my mind what happens, and the recovery process.
Remove one drive at random (simulating sudden death), and slot in a new one. It took several hours to rebuild.

Having a RAID is all well and good (raid is not a backup), but if you don't know how to recover and when, it is less than useful.
 
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GhislainG

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The first step is to replace the failed drives; then you should be able to rebuild the array..

 
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AmeedMv

AmeedMv

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It is not exactly acting as a backup in my case. It is being used to store large amounts of media in a small production company. So it itself is the main thing we have here and also the backup. Now I know that sounds stupid as well it is stupid. So should I replace the two failed drives and try a rebuild from within the NAS Utility?
 
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AmeedMv

AmeedMv

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So should I just get a pair of new HDDs and try a rebuild? Please note that 2 drives are degraded.
 
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USAFRet

USAFRet

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What does the NAS OS and user manual say specifically about a failed drive?
Almost certainly..."replace them"

But do it one at a time.
 
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AmeedMv

AmeedMv

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Okay. Thanks for the information. So I guess I will try that option then. Is there anything I should be careful about when swapping the drives?
 
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USAFRet

USAFRet

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Can we assume that the system has identified the broken drives, and that you know which ones they are?
 
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AmeedMv

AmeedMv

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Yes, I can identify them via the NAS Utility and physically as well.
 
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