Data recovery services on a parity drive?


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I won't bore anyone with the details, but after some compounding bonehead mistakes I'm currently stuck with some drives that will not spin up (neither in my server nor a USB enclosure).  Three drives: two data drives and one of my two parity drives.  Not sure if this make sense, but if I wanted to use a data recovery service on that parity drive would I then be able to replace the two dead data drives and not have any data loss?  

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Theoretically, yes. Practically, I don't think so.

 

Theoretically, you can use the recovered parity + existing parity to rebuild the 2 data disks.

Practically,

  • Your parity does not contain actual data ("actual" in the sense of for example, image files that can be displayed or video files that can be watched etc.), which makes data recovery even more complicated because the technician has little clues as to whether the data was recovered correctly or not. In a sense, the recovery is basically repair, replace, clone. Any imperfection can be at best losing a file and at worst losing the file system.
  • There is no guarantee that another disk won't fail while rebuilding. Not sure what mistakes you made but if the underlying root cause has not been resolved, it may very well rear its ugly head. Again, because parity does not contain actual data, if that happens, you just lose more data (unlike if you recover a data disk, you are guaranteed the data on that disk).

This is a very difficult decision to make. [Pay for 1 with the risk of having to pay for 3 or more] vs [Pay for 2 in full].

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13 minutes ago, testdasi said:

Theoretically, yes. Practically, I don't think so.

 

Theoretically, you can use the recovered parity + existing parity to rebuild the 2 data disks.

Practically,

  • Your parity does not contain actual data ("actual" in the sense of for example, image files that can be displayed or video files that can be watched etc.), which makes data recovery even more complicated because the technician has little clues as to whether the data was recovered correctly or not. In a sense, the recovery is basically repair, replace, clone. Any imperfection can be at best losing a file and at worst losing the file system.
  • There is no guarantee that another disk won't fail while rebuilding. Not sure what mistakes you made but if the underlying root cause has not been resolved, it may very well rear its ugly head. Again, because parity does not contain actual data, if that happens, you just lose more data (unlike if you recover a data disk, you are guaranteed the data on that disk).

This is a very difficult decision to make. [Pay for 1 with the risk of having to pay for 3 or more] vs [Pay for 2 in full].

Thanks for responding.  The mistake was using a modular PSU cable from my old PSU/build in my new PSU/build, leaving me with five drives that won't spin up (two are net new to the system).  So that won't be happening again.  But if that's the case regarding repairing the parity drive, then yes it's probably safer to just bite the bullet on repairing the two data drives.

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So, in this situation, I have 5/8 drives in my array still spinning up and presumably with no data issues: dual cache, parity1, and 2of4 disks.  Is there any scenario where I could rebuild partial data to a new drive using the parity drive, or should I just clear the drive and start fresh?

 

Also, will i have any issues keeping the existing data on my cache pool and two working drives when i start a new array config?

 

Thanks in advance.

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6 hours ago, jamesp469 said:

Is there any scenario where I could rebuild partial data to a new drive using the parity drive,

Yes, if you can get one of your failed data drives working completely intact. Parity uses ALL drives, not just the parity drive to rebuild data. At the moment you have 3 dead drives and with dual parity your system can recover from 2 dead drives. If you can recover one of the dead drives, doesn't matter which one, you can rebuild. Since the dead parity doesn't actually contain any sensible data, it makes much more sense to attempt recovery on one or both of the dead data drives, and if that succeeds and nothing is written to it, you should be able to recover the the other data drive.

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12 hours ago, jamesp469 said:

The mistake was using a modular PSU cable from my old PSU/build in my new PSU/build, leaving me with five drives that won't spin up (two are net new to the system). 

I seem to recall hearing about another case where this happened.  As I recall, the electronics board(s) was/were fried.  Believe it or not, this is something that can be recovered from with certain models of hard drives rather easily-- you just replace that board with another one.  With other models, the problem is more complicated because the board is programed during manufacture to match that drive.  (A google search should give more details on the entire situation.)  

 

If the data is truly that valuable, I would contact a data recovery company and discuss the situation with them.  (Have full label information on all of the drives available!)  I would start with recovery of the data drives first.  The reason is easy to explain: the information on the parity drive(s) is the result of a math operation as described here (for single parity):

 

     https://wiki.unraid.net/index.php/UnRAID_Manual_6#What_is_unRAID.3F

 

For dual parity, you need a graduate level understanding of Matrix algebra. 

 

As explained, you need to recover one of these three drives.  It does not matter which one. 

 

In the case, where you feel the cost is not worth the costs involved with using the data recovery company, you could try to do it yourself.  It basically involves replacing that electronics board.  You research the drives involved and pick the most likely candidate to try first.  Buy the board (E-bay would be a good to start looking) and swap boards. 

 

EDIT:  It should go without saying this, DO NOT USE THIS ARRAY until you decide what you are going to do!  Any write to any other disk will invalidate the parity information on the currently dead dparity drive.  

Edited by Frank1940
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16 hours ago, Frank1940 said:

I seem to recall hearing about another case where this happened.  As I recall, the electronics board(s) was/were fried.  Believe it or not, this is something that can be recovered from with certain models of hard drives rather easily-- you just replace that board with another one.  With other models, the problem is more complicated because the board is programed during manufacture to match that drive.  (A google search should give more details on the entire situation.)  

 

If the data is truly that valuable, I would contact a data recovery company and discuss the situation with them.  (Have full label information on all of the drives available!)  I would start with recovery of the data drives first.  The reason is easy to explain: the information on the parity drive(s) is the result of a math operation as described here (for single parity):

 

     https://wiki.unraid.net/index.php/UnRAID_Manual_6#What_is_unRAID.3F

 

For dual parity, you need a graduate level understanding of Matrix algebra. 

 

As explained, you need to recover one of these three drives.  It does not matter which one. 

 

In the case, where you feel the cost is not worth the costs involved with using the data recovery company, you could try to do it yourself.  It basically involves replacing that electronics board.  You research the drives involved and pick the most likely candidate to try first.  Buy the board (E-bay would be a good to start looking) and swap boards. 

 

EDIT:  It should go without saying this, DO NOT USE THIS ARRAY until you decide what you are going to do!  Any write to any other disk will invalidate the parity information on the currently dead dparity drive.  

Thanks, I've sent one of the data drives in to get tested and see if it a PCB replacement would fix it.  Hopefully it does, and then I can re-install that plus two drives to replace the parity2 and other data drive and hopefully be back in business.

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UPDATE: I was able to get one data drive repaired, and I expect it to be delivered back here tomorrow.  Can someone point me to the correct process for turning my system back up?  I have brand new drives to replace the blown 2nd parity drive and the other data drive that was not repaired, as well as a new drive to replace the repaired drive once my parity is rebuilt.

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There is a bunch of information needed to give clear guidance. I suppose the first step would be to physically install all the working drives, boot the server, and take a screenshot of the MAIN gui page, and collect diagnostics. The next steps are dependent on what state the array is in at that stage.

 

Was the drive recovery service able to give guidance on the further use of the repaired drive? Were they confident it would continue working after the repair for a significant period of time, or did they say to recover what you can and then quit using it? The answer to that question may change the preferred order of operations for recovery.

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16 hours ago, jonathanm said:

There is a bunch of information needed to give clear guidance. I suppose the first step would be to physically install all the working drives, boot the server, and take a screenshot of the MAIN gui page, and collect diagnostics. The next steps are dependent on what state the array is in at that stage.

 

Was the drive recovery service able to give guidance on the further use of the repaired drive? Were they confident it would continue working after the repair for a significant period of time, or did they say to recover what you can and then quit using it? The answer to that question may change the preferred order of operations for recovery.

The repair service recommended cloning/moving the data off of the drive whenever possible.  It was only a PCB replacement, so not sure if that was a liability-relief statement or not.

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