Certainly, you should try again with a different USB drive
All working now, thanks. I've bought a small branded SSD in an external enclosure and it seems to be working fine.
Edit - not working once I installed the develop version :-(
Jan 28 16:58:29 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:30 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:33 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:33 connmon: SQLite process reported error(s).
Jan 28 16:58:34 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:35 kernel: DROP IN=ppp0 OUT= MAC= SRC=103.141.137.236 DST=212.159.74.61 LEN=40 TOS=0x00 PREC=0x00 TTL=238 ID=25567 PROTO=TCP SPT=52707 DPT=8609 SEQ=2210072643 ACK=0 WINDOW=1024 RES=0x00 SYN URGP=0
Jan 28 16:58:36 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:37 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:38 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:39 connmon: SQLite3 failure: Parse error near line 5: disk I/O error (10)
Jan 28 16:58:39 connmon: SQLite process reported error(s).