All Shares appear to be missing [ReadyNAS Ultra 2; Radiator 4.2.28]

Some weeks ago I (possibly stupidly) ignored a reported filesystem consistency check failure.  Have had the check pass successfully since.

Today I discovered that I can no longer connect to any of my shares (via SMB) from any Windows 10, Mac, or iOS devices.  I can access the one share that I have made available via HTTP.  I can access the Admin UI.

I went to have a look at the logs, and that screen says 'No logs available'.  (I do have a subset of logs available form a remote syslog server).  This line looked interesting :-)

Nov 15 20:47:34 TMF-UK-PL-STORE01 syslogd:  /var/log/user.log: No space left on device

SSHing in it appears that /dev/md0 is out of space:

Store01:~# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/md0               4176564   4176564         0 100% /
tmpfs                       16         0        16   0% /USB
/dev/c/c             2903445768 375335472 2528110296  13% /c
Store01:~#

Help with how to proceed from here??

Thanks in advance,

Rob.