I built myself a linux-based NAS. It has several drives of various sizes and ages in an LVM configuration, with 800GB or so of data. The data is served using a simple samba server.

This was working flawlessly, but after physically moving it, it has developed a strange fault: Whenever I do something on the server to cause disk activity, the entire machine freezes hard. This has the effect of killing any open network connections to the box, and generally making it useless.

If I leave the machine for a few minutes it seems to come right again, but obviously this isn't really a solution.

There are no error or warning messages in syslog, or the kernel logs. If I power the machine on, and leave it, it runs for several days without locking up. After that time I stopped testing.

It doesn't freeze instantly - obviously it doesn't freeze while booting, and I can normally log in via SSH and start poking around in a few log files for a couple of minutes before it dies.

My question is:

What diagnostic tests can I run to determine the casuse?