Well, not quite how I wanted to start the weekend...
Went to watch something from my fileserver, on the PS3, and it just sat there doing nothing. Pressed stop, which responded instantly and back to the file-browser, so tried again with the same result.
Tried to SSH to the fileserver, nothing, although it was still pingable. So, tried plugging a monitor and keyboard into it, with absolutely no luck. Power-cycling was the only option left, so tried that...
As soon as it powered back up again, the monitor flickered into life, and I got the BIOS screen, went through the normal checks but the ominous feeling started when I saw it confirm the presence of three working disks (there are four in there), which was compounded by seeing the nice friendly "you have no operating system installed" error-message.
Now, given that the server is RAID-5, I'd assumed that losing a disk would be fine, and it would still boot up in a degraded state with all of the data intact - unfortunately, using software-RAID, it doesn't look like this is the case!
So, I now have 3 options, which I'll be trying in order:
1) Boot the system up, with three working drives connected, using a Linux LiveCD on USB key, and see if it can see any data.
2) Replace the broken drive, and see if the software-RAID system rebuilds the array from the three working disks.
3) Write off 2.3TB of data as lost and irretrievable (unless I fancy paying silly money for a company to do it - I don't), and rebuild the system with the new disks I've bought today, ie. the upgrade I was planning to do anyway (but preferably without losing all of the data in the process).
Fingers crossed #1 or #2 work, then I can make a backup of the data, and then go onto #3 without losing the data...