ReadyNAS NV+ v2 - "no data volume" since upgrading disks

Hi all,

We have attempted to increase the storage on our NV+ v2 by replacing the four existing 1TB drives with 3TB drives (confirmed the new drives are compatible). The first 2 were replaced successfully so we went ahead and replaced the 3rd one 4 days ago and somewhere between then and yesterday morning the data volume has become unreachable.

The console was also not accessible (via the browser interface) so I needed to do a hard reset to bring it back up

I ran a disk scan from the boot menu which found errors on disk 4 (one of the original disks) and tried to swap it with a new HDD but the new disk was not being initialised (though the box displays a message on the LED confirming that a new disk has been added).

I tried an OS Install but it seemed to hang on "Installing addon". After restarting the box it looked as though the OS reinstall had completed (settings/password were set back to defaults etc)

It's a RAID5 config

Our users' support agreement expired a few years back so I'm hoping to get some more ideas from the community on what to try next.

Thanks very much in advance!

Dean