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ReadyNAS 214 "Remove inactive volumes to use the disk. Disk #1,2,3,4."
Hello, I recently updated my firmware on a ReadyNAS 214. Next time I looked I got a degraded volume error on Drive bay #1. I have 4 WD Red WD30EFRX drives but when I searched for a replacement I wa...
mharring54 wrote:
Okay - understanding this is what's tripping me up.
Here's a brief (and simplified) explanation.
Sector X on disks a, b, and c are for data. The corresponding Sector X on disk d is a parity block. This is constructed using an exclusive-or (xor) of the three data blocks You can think of this as addition for our purposes here.
Every time Xa, Xb, or Xc are modified, the RAID also updates Xd.
So Xa + Xb + Xc = Xd.
If disk b is replaced, then Xb can be reconstructed by
Xb = Xd - Xa - Xc
Similarly, the contents of any of the other disks can be reconstructed from the remaining 3. That is what is happening when the RAID volume resyncs.
The reconstruction fails if
- the system crashed after Xa, Xb, or Xc was modified, but before Xd was updated.
- two or more disks fail (including a second disk failure during reconstruction).
- a disk read gives a wrong answer (instead of failing). This is sometimes called "bit rot".
- the system can't tell which disk was replaced.
The RAID system counts up the writes to each disk (maintaining an event counter for each disk). So it can detect the first failure mode (because the event counters won't match). When it sees that error, it will refuse to mount the volume. That is a fairly common cause of the inactive volume issue.
Often it is a result of a power failure, someone pulling the plug on the NAS instead of properly shutting it down, or a crash. The RAID array can usually be forcibly assembled (telling the system to ignore the event count mismatch). There can be some data loss, since there were writes that never made it to some of the disks.
Two or more disk failures sounds unlikely, but in fact it does happen. Recovery in that case is far more difficult (often impossible, or cost-prohibitive).
Figuring out what happened in your case requires analysis of the NAS logs. If you want me to take a look at them, you need to download the full log zip file from the NAS log page. Then put it into cloud storage (dropbox, icloud, etc), and send me a private message (PM) using the envelope icon in the upper right of the forum page. Put a link to the zip file in the PM (and set the permissions so anyone with the link can view/download the zip file).
That you are seeing volume "data" and "data-0" means the OS can't assemble all the drives in one volume, but does recognize that there is something that needs to be assembled and has labeled them separately. That usually means they are out of sync (something changed on some, but not all, drives in the RAID). Both contain parts of your actual "data" volume, so don't delete either of them. But because file contents are spread among all drives, you can't just go into either and get data. StephenB can help you try to manually assemble them into one via the command line. There could end up being a few corrupted files, but most will likely be recoverable.
I think you are prevented from formatting when you have an invalid volume. It's a way the OS keeps you from doing something stupid that makes recovery impossible. Just adding another drive will not fix your problem, anyway. It's too late for that. If the old drive can be read at all, cloning it to the new one may help with the recovery.
If you can assemble the volume, you are going to want to save off all the files and re-format the whole volume, so you are going to need somewhere to put them. After you've restored everything, that somewhere can become your backup, so size it appropriately.
Thanks Sandshark,
You wrote:
"If you can assemble the volume, you are going to want to save off all the files and re-format the whole volume, so you are going to need somewhere to put them. After you've restored everything, that somewhere can become your backup, so size it appropriately."
Yes, I guess that is best practice. I have data spread across several USB external HDs but I never trust them bc WD often fails. So, I bot 12TB of these WD Red drives to secure my data on an NAS and now I need to duplicate it with another large harddrive? Are backups possible by just plugging in the USB port on the ReadyNas drive bay?
I'm wondering when all is said and done whether the new WD 3TB Red Plus drive I bought will be necessary to replace the degraded drive?
Thanks
Michael
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