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Forum Discussion
Software to Recover array from each Hard drive outside of Readynas system?"
Is there a recovery software that can rebuild an array from individual drives outside the Readynas system? I have a readynas NV+ V1 and the system is not booting. I have tested each drive and...
Your NV+ is using RAID-4. It is similar to RAID-5, except all the parity blocks are placed on one disk. The parity blocks are actually written to an unpartitioned section of the drive.
http://home.bott.ca/webserver/?p=306 gives some info on how to mount an array in a standard linux system.
There are recovery packages that claim Netgear support, though I haven't used any of them - so I have no recommendations. Hopefully others will chime in.
I had to do a second take on this response before it sunk in exactly what you are saying.
Normally in raid 5, if a hard drive fails in a 4 drive system, the remaining hard drives can recreate the data regardless of which 3 you use.
You are saying that all the parity is on a single disk? So if that is the case, when you mount to linux can read the information right off the disk without " rebuilding" anything.
In the case of the parity disk failing, all the data should be recovered however if the drive that failed is not a parity disk, that means the data is not recoverable using this linux method? Is that right?
Since this is nonstandard raid(xraid), do you have any tools that know how to rebuild the information using the parity drive? Also, what drive is the parity drive in a 4 drive system?
Is it always the same drive? In my case, drive #3 and #4 are suspect.
Thanks.
If the parity disk is not the disk that fails the system would still boot fine. There would have to be additional problems e.g. with another disk, or a problem on the root volume etc. to still have issues.
In situations like yours a data recovery contract with support could be used. Support would check and see what the best way forward is and may suggest cloning (support can attempt cloning disks using a Linux tool designed for cloning failing disks but if support does that we'd have to charge extra for that, so most users prefer to do the cloning - if required - themselves).
miogpsrocks wrote:
Normally in raid 5, if a hard drive fails in a 4 drive system, the remaining hard drives can recreate the data regardless of which 3 you use.
This is also a property of RAID 4. If only the parity disk fails, it can be recreated from the other three. If a data disk fails, it can be recreated from the remaining data disks plus the partity disk.
So the recovery properties are the same, this is just matter of how the parity blocks are organized. The disadvantage of RAID-4 is that any writes require updating of the parity disk. So the write load on the drives is uneven. That can reduce throughput, and potentially create more wear on the parity disk. RAID-5 spreads the parity blocks across all disks to solve those issues.
Mounting the volume in linux (using the link I posted) does allow the parity blocks to be used for recovery if needed.
miogpsrocks wrote:
Since this is nonstandard raid(xraid), do you have any tools that know how to rebuild the information using the parity drive? Also, what drive is the parity drive in a 4 drive system?
xraid is actually standard RAID underneath. Generally with RAID recovery tools there are some RAID parameters that either the tool discovers or which need to be manually entered. I'm not sure what those are (I haven't needed those tools), but Netgear folks can/will provide them if you need them.
The parity disk is usually disk 4. "usually" because it depends in part on this history - sometimes users move disks around.
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