It is shockingly easy to move an iSCSI LUN from one Netgear ReadyNAS OS 6 device to another.  This exercise is performed on version 6.7.2, the latest version at the time of writing.

Netgear's official method for migration is to create new new iSCSI LUN on the destination device and mount it in your operating system -- I am doing this in Windows.  Then use robocopy or your favorite mass copier to copy the data from the old LUN to the new LUN.  This could take a long time if you have a lot of data, especially if your data consists of a lot of small files (photos, phone videos, etc.)  My data is a healthy mix of small (photos, music, and such) and large files (ISOs, VDI/VHDs, etc.) as well as a lot of files encrypted with EFS.

This is gonna take for-e-ver.

Logging into my NAS through SSH and poking around I found there is an iSCSI backing store file for the LUN.  It is conveniently located in /data/(name of your LUN)/.iscsi/ with the name iscsi_lun_backing_store.  Simple!

I was originally copying the non-iSCSI files from the old to new NAS using rsync, but the rsync configuration does not allow you to select the root of your data store (/data) but instead you have to select each and every share.  When I tried using SMB, I found I could select /data and about 13 hours later I had an exact copy of my old NAS data on the new NAS.

INCLUDING the iscsi_lun_backing_store file and the associated .serial_number file.

So, the process became to create the new iSCSI LUN on the new NAS with the same name, size, and block size configuration as on the old, then run the backup task on the old.  I let that rip and sure enough the backing store file had copied.  Then I connected to the new LUN, took a quick dash into diskpart to bring the drive online and holy-o-crap!  I had two identical drives mounted on my Windows desktop, the second having an intact NTFS file system and randomly-select files all check out.

The next step is to see if the app data for Plex will be usable in the same way as all of its directories copied over, as well.  I installed Plex and disabled it before the backup migration.  The hope being that upon starting up, all of its databases and configurations will be right where expected, and I will now have a complete Plex mirror of the old NAS.  This would be the second and last step in data migration which would make my life (and this process) much easier.

UPDATE: Moving Plex to the new NAS was a little more work as the actual Plex application files (database, bundles, etc.) are stored in /apps.  I copied the entire plexmedia directory (~110GB) to the new NAS via an external hard drive.  Once I started the Plex app on the new NAS it loaded everything as expected.  I had to make minor settings tweaks, such as the local interface, but otherwise all seems to be working fine, including the device logging into Plex.tv servers.  One important thing I forgot was I had upgraded the Plex server on the old NAS.  While the new NAS indicated the correct version within Plex, the system detected otherwise.  Installing the upgrade version went without a hitch.

Nothing short of a Christmas miracle!