Apologies for cross-posting this from the ubuntu forums, but it feels like questions often go completely unanswered there.
I've had this problem a few times now, and it's really worrying me, as it means I have to hard reset. Normally Ubuntu is so stable!
I have samba set up on an Ubuntu server (11.04), sharing a directory mounted on a RAID 5 array managed by mdadm. If I access this via a Windows PC, and modify a large number of files quickly (e.g. some bulk edit operation, in this case applying changes to tags of music files), the server becomes completely unresponsive.
By that I mean the connection is lost, I can't SSH into or ping it, and pressing keys on the keyboard does nothing (which I can see if I log on locally first; after the lock up the terminal doesn't respond at all).
I left it for about an hour last time this happened and it didn't get any better, so I had to hard reset it, which I really don't want to do again. Also, just waiting isn't really a good solution, I'd expect it to always be responsive.
This has happened 3 or 4 times now, and seems completely repeatable - I get around it by modifying smaller batches of files. That said, it happened just now after copying about 10MB to it.