Well, sortta. You can back up the configuration via the Settings page of the GUI and data via backup jobs. Some app configurations will be backed up and some apps will require you to separately back up their data, especially if it's in a database or was installed via SSH instead of a ReadyNAS-specific app. You cannot back up the apps themselves. Then you swap out the drives and create a new volume. Be sure to re-install the apps before you restore the backed-up configuration. Since you aren't destroying the original volume, you can always swap the drives back and get anything that you forgot to back up. With two volumes, you could replace only one of the drives now and re-use an old one, but that would make recovery from the old one impossible.
FWIW, RAID0 is a very vulnerable configuration, Any loss on one drive kills the data on both. You may want to consider setting up the drives as separate volumes. That means you have to manually distribute content between the two, but it makes recovery from a drive failure easier. Note that it will still have no redundancy (which really isn't enough to protect your data, but helps) I hope you already have and plan to continue to have a backup unless the NAS is already only backup data.
sounds like you might not have a backup (another 2 bay nas or 2 12TB USB disks for backup at minimum recommended and required to replace the disks in raid0) app backup is lot more complicated as they are in hidden folders (i usually only use readynas as backup units so haven't used anything more then the built in features like snapshot and backup tasks)
you may want to consider a 4-5+ bay nas to give your self a bit of redundancy (3x12TB disks raid5 < x-raid auto) but that is still not a backup thought (does allow online disk replacement or/and replace disks with larger disks) and you wont have to re set up the nas every time you want to add more space or replace a failed disk
or have 2x2 bay nas's or 1 nas and 2 USB external hdd backups
make sure you setup monthly disk scan (say 1st each month) and scrub (7th each month) , make sure the Volume and share folders have checksum enabled when you create them to allow the scrub to be effective at reporting corrupted data (in raid1 or 5/6 it will attempt an auto repair if errors are detected) and setup email notification (recommend not use google as login as its tokens expire,, hotmail/Microsoft does not seem to expire its login tokens, you can add more then 1 email for notification in the list)
if no backup is been used, recommend a 5+ bay nas with 4-5 disks in raid6 to minimise total data loss but not eliminate it (raid6 is still not a backup but significantly safer at replacing disks as you still have 1 disk redundancy when rebuilding and handling 2 disk failures) to use raid 6 leave one disk outside of the unit when you set it up the readynas, once setup turn off x-raid insert the new disk and add parity disk once it starts adding the disk you can turn back on x-raid that will transform into raid6 (or turn off x-raid with all disks inserted and destroy the volume and recreate it as raid 6 then turn x-raid back on) readynas makes this more compacted then it needs to be (it should ask for redundancy amount like it used to on OS5 when 4 or more disks are installed)
raid0 is very risky especially without a backup (very explodey if one disk fails)
