Parity Drive - Useless without other drives?

[UnRaid_11317]

Is there any recoverable or identifiable information from a single parity drive on its own, out side of the array? Can any information be recovered from it? Files? File lists? Directory structures?

 

Someone pulled the parity drive rather than one of the blank extra drives for a return. Should I be worried about a possible data breach or the ability for anyone to recover any data off that parity drive that is now out in the world or is the information on it useless without the array?

 

[bonienl]

The parity disk itself does not contain any files or folders. It holds the calculated checksum over the data disks.

 

You can simply insert a new parity disk and do a parity rebuild, no user information is lost.

 

[pwm]

The content of the parity is computed on blocks from the data disks. But there are still situations where it can leak information.

 

If you have a machine with one data disk with content and zero or more data disks with just zeroed information, then the information on the parity disk will be based on the content of that single data disk - which means file data will leak.

 

Same if one data disk is full while the other data disks are empty and have earlier been zeroed or have the factory-default pattern for unused blocks.

 

Same when the parity disk and one data disk is larger than the other disks - then the last part of the parity disk is computed from the content of just one data disk.

 

So even if the parity drive doesn't have a file system and store actual files or file lists, it should still be treated as if it contains sensitive data, because there exists situations where information may be retrieved.

[UnRaid_11317]

Thank you both for your answers!

 

PWM just to clarify: The missing parity drive is from a 20 drive array with 3 drives that are 3TB and the remaining 17 drives are 4TB, The missing parity is actually drive #2 in a 2 parity configuration. Both parity drives were 4TB.

 

So if I understand both pwn and bonienl correctly: in this particular situation there is no opportunity for any information (Files, File Names, Directory structures) to be retrievable or recoverable from the missing drive and I can tell everyone involved that there is nothing to worry about and we do not need to track down this drive.    

[John_M]

The fact that it was part of a large array, coupled with the fact that the Parity2 algorithm is somewhat more complex than a simple XOR, makes it extremely unlikely that anything could be recovered from it.

[Frank1940]

You might want to read through this thread:

 

     https://lime-technology.com/forums/topic/51362-pq-or-dual-parity-in-detail/  

 

I would hazard a guess that an agency with the resources of the NSA might be able to recover some data under a some weird set of  theoretical circumstances where only single drive had any data (besides zeros) on a range of sectors but determining where those sector ranges were would be mind boggling.  If you are the target of such an organization, I would suggest that the loss of this Parity 2 disk would be the least of your worries...

[pwm]

8 hours ago, UnRaid_11317 said:

Thank you both for your answers!

 

PWM just to clarify: The missing parity drive is from a 20 drive array with 3 drives that are 3TB and the remaining 17 drives are 4TB, The missing parity is actually drive #2 in a 2 parity configuration. Both parity drives were 4TB.

 

So if I understand both pwn and bonienl correctly: in this particular situation there is no opportunity for any information (Files, File Names, Directory structures) to be retrievable or recoverable from the missing drive and I can tell everyone involved that there is nothing to worry about and we do not need to track down this drive.    

 

With 17 drives of same size as the parity, there will generally be very hard to extract any information - a single media file overlapping a critical file will very effectively destroy the recovery options since media files uses compression algorithms that introduces a very high independence between bits in the file.

 

And just because a data disk has 10 GB free space doesn't mean it's the last 10 GB of the surface that is currently unused - earlier file delete/overwrite operations may result in the currently free space being somewhere in the middle of the addressable range of the disk.

 

So unless you store data requiring the highest military security levels, I would say that you can sleep quite well despite having lost track of that parity drive.

[UnRaid_11317]

Thank you for the follow up everyone!! I really appreciate your help!