Can I shelf a JBOD volume for later?

Sorry for the late reply, I've been having login issues.

The warning saying it's going to destroy the volume when you intend to export, not destroy, is a programming error -- it points to the wrong warning or is a bad cut-and-paste by the programmer, as it's identical to the one when you are actually destroying a volume.  But it does do an export.  I reported the error long ago and was ignored.

If you forget to EXPORT the JBOD volume, you can boot with just that drive.  It will show the main volume as "missing" and apps and such won't work, but your JBOD data will be accessible.  That works because the OS partition is duplicated on every drive.  But that does mean that any changes you make to the NAS after removal (like a password change), won't be there.  At that point, you should back up all the files.  Alternately, you can then EXPORT it (though any other time, exporting the only volume is a really bad idea).  Once you do the export, it won't boot by itself again, but it will import to another volume.  Thus, backing up the files before doing the export is the best practice, just in case something goes wrong with the export or import.  If something were to happen to your main volume that prevents importation, you could simply create a new one with a single drive and do the import to it (which is also how you recover from an inadvertent export of the main volume)

I have not figured out what marks a volume as exported so you can undo it by a method other than import to another ReadyNAS or mark it is exported outside ReadyNASOS.

One thing to keep in mind with export/import is that there can be no volume or share names the same on the imported volume as on the main one importing it.  (Well, there can be shares, but they'll end up invisible at anything other than SSH level.)  File and folder names below share level are not subject to this limitation.

The EXPORT function is not covered in any Netgear documentation I've found.  You can read about my experiments with it at Experiments-with-exporting-and-importing-a-volume-in-OS6-7-1.  As best as I have been able to tell, there have been no changes made since then (since the warning error wasn't even corrected).

Now, all that said, a NAS is not really intended to be used that way and an external USB drive is a better solution.  That's especially true now with the RedayNAS being EOL -- use a format on the USB drive that can be read by your computer in case the NAS dies.