If you have Seagate Barracuda 7200.11 disks from 2008 or 2009 you should be very concerned. These disks have a faulty firmware and also the disk surface is problematic. Sector errors are developed very quickly and the firmware will fall on its face.
The symptoms is a 7200.11 disk that either isn't detected by the BIOS anymore (BSY busy error) or reports itself as 0GB in size (0 LBA zero error). Sometimes the disk shows up again and can be accessed for a few moments and a couple of megabytes and goes away again with media error or BSY busy.
The failure rates of 7200.11 are reported to be as high 40-50%. And even if it ran for weeks or months doesn't mean it wont have the problem. Quite to the contrary. It most likely develop the one of the errors soon. Claudio lost a number of disks in his raid array and I just lost the one from my desktop computer.
Anyway, here are my recommendations:
1) Check whether you have any Seagate Barracuda 7200.11 with 500/750/1000/1500GB in your servers or desktops
2) If you have any, then backup the data *right now* to some safe disk or media
3) Replace the 7200.11 as soon as you can with some other brand and model, even if the Seagate tool/website says you disk is not affected
If you already have lost a 7200.11 and still have the disk or if it happens from now there is a way to recover your data. Do *not* do the firmware update that is recommended by Seagate. The recovery process is complicated and involves accessing the disk controller through a debug port and get the firmware into debug mode. All the nasty details in [1] and [2]. You have to cautious with the procedure though. There are some commands shown in the thread that should *not* be executed or further data loss may happen. Read up to page 35 of the forum and only then start your own attempts. "avico" is the guy to look for his posts.
I've done the recovery on two disks successfully, including one that had many fatal sector errors. So if you've got a bricked 7200.11 I've got a working setup and may be able to help you quickly to recover your data.
[1] http://www.msfn.org/board/solution-seagate-7200-11-hdds-t128807.html [2] http://sites.google.com/site/seagatefix/