Hard drive failure - Could unused sectors be fine?

So we had a hard drive failure today and it got me thinking. It was a 200GB, sata, hard drive and since it was installed there has only been one 20 GB ext2 partition on that drive.

Could the rest of the drive be fine? No other partitions on that drive only unused free space.

This had filled up the syslog, stating different sectors every now and then:

sd 0:0:0:0: SCSI error: return code = 0x00040000
end_request: I/O error, dev sda, sector 4093207
Buffer I/O error on device sda1, logical block 491606
lost page write due to I/O error on sda1

Of course we replaced the drive, this is out of sheer curiosity.

The problem here isn't if the rest of the blocks on the drive are ok or not. The problem here is if the drive is showing bad blocks to the host then it means that the drive is out of spare blocks so it no longer has the ability to remap a bad block. This may or may not be the situation with this drive but you can have a look at the S.M.A.R.T. information from the drive to see if this is the case or not. In particular you want to look at attribute 05 Relocated Sector Count. If this number is high it would confirm that the drive is having to remap a lot of sectors.

Wikipedia has a good article on S.M.A.R.T. which includes all the known attributes.

In either case I think I would just replace the drive.