Moving disks between NASes

There is a frequent question I’d like to address: is it safe to move disk packs between identical NASes?

The full version may well go like this

Last night my Ready NAS (RND4000) stopped working. It looks like a fault in the power supply…I would like to recover some…files.

One option I see is a friend of mine who owns the same system. Is it an option to shut down his NAS, remove/replace the installed disks with the disks from my NAS and copy the data? Or are any obstacles in the way?

All in all, it should work. Possible obstacles include

  1. Different NAS models. Obviously, the NASes must be of the same vendor, same product line, and in most cases models must be fully identical.
  2. Different firmware. Preferably, both NASes should use the same firmware version. However, once the unit fails, there is no way to determine exactly which firmware it was running at the time of crash. In this situation, the recipient unit is better be patched to the latest firmware. The latest firmware will typically accept disk packs created by older versions.
  3. Damage to the disks, either physical or logical. When the power supply blows, it may take the NAS with it; also the disks may or may not be damaged by electrical transients. If this happens, the replacement NAS is not going to work, obviously.

If you think none of this applies to your situation, you may give it a go.

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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.

 

iSCSI

Sometimes, there are problems with iSCSI LUNs hosted on the NAS. iSCSI is a protocol of presenting some storage over the network (over the Internet for i) as a hard drive (a SCSI hard drive). i + SCSI = iSCSI. With NASes, some part of the NAS disk space is configured to be accessible over iSCSI. Each distinct piece of disk space presented over iSCSI is called LUN. The PCs connected to the NAS sees an iSCSI LUN same as its own physical drive. This is all you need to know about iSCSI, unless you want to dig deeper. If you want more, start with Wikipedia article.

There are two types of problems with iSCSI.

First type is illustrated on the QNAP forum – iSCSI LUN turned to RAW,

[I] have had iSCSI on my TS-212… Is see the iSCSI drive, but when I try to access the drive Windows says that drive needs to be formated before it will be used. When I checked the file system it says that disk is RAW instead of NFTS…

This case does not look like it requires any recovery on the NAS side. The faulty “disk” should be treated in the same was as  one would treat a local drive. A plethora of software is available for you to choose from to work with RAW filesystem in Windows.

Second type of the problem is when the “disk”, that is, iSCSI LUN, is no longer visible, or cannot be “attached” to the PC. Depending on the exact setup of the NAS, recovery may be quite a complex process, beyond the scope of Home NAS Recovery. If you have this type of problem, you probably should be looking for a data recovery service.