So I shut down Mysql, ran a repair/optimise on all and everything seemed ok
An hour later, some more tables came up with marked as crashed
I checked the logs and saw lots of errors like this:
130318 16:33:56 [ERROR] /usr/sbin/mysqld: Incorrect key file for table './x/jos_session.MYI'; try to repair it
130318 16:34:06 [ERROR] /usr/sbin/mysqld: Table './x/jos_session' is marked as crashed and should be repaired
I checked the tmp folder, it had some 899mb free, so it wasn't that, but repairing, the tables just didn't seem to "hold"
I've now changed the mysql tmp folder to another location, to see if it helps, but any tips?