How long to rebuild?

There is a story of routine drive replacement going belly up

[I] have a Netgear ReadyNAS NV+ (RND4410)… [containing] four 1TB-disks…I changed all disks to 2Tb-disks. As it’s a X-Raid NAS I just pulled the disk from slot 1 and mounted the first new 2tb disk…[NAS] started the sync… 3 days later it still said syncing and I could still not reach the web-interface.

I pulled the plug and rebooted the NAS.

It did a check on the NAS volume and then it said booting with the LED on slot 1 still blinking.

[30 hours later it was] stuck on Booting and can not reach it in the web-interface.

despite the NAS owner specifically states that

No smart errors detected before start.

The case still looks very much like a failure of the second disk during rebuild. The most likely reason of a NAS not being able to complete the rebuild while blinking its disk LEDs is a read failure on one of the remaining drive. The X-RAID mode in ReadyNAS is essentially a RAID5, so once the disk fails, the NAS is supposed to remain online and rebuild the content of the failed disk once said disk is replaced. Observed result is that the NAS does not even remain online. Leaving aside the possibility of the new disk being a dud, another likely reason is that the second disk failed to read a block and the NAS is now locked up, endlessly retrying the read.

What could be done in this situation?

  1. Pull the new disk out and try to start up the NAS. If the NAS starts, shut it down again and try with another blank new disk. This rules out the possibility of using a dud as replacement.
  2. If that does not work, try and put the original disk back. This further rules out any  incompatibility of the new disks with the NAS. The entire batch of new disks may be DOA or incompatible. These things happen, albeit rarely.
  3. If putting the original disk back does not help, yet another attempt should be made without the disk at all (with both original and replacement out). If the NAS comes online, first thing should be made is to back up its content, most starting with the most important.

If none of this works, we have Home NAS Recovery for you. You should give it all the disks which were in the NAS all the time. That is, you’d better leave out the original disk which was removed and any replacement disks. The only set of disks guaranteed to be in sync with each other are the disks which were never removed from the NAS.