This evening I started getting the following error when trying to write to
a volume on a SCSI drive:
	[root at lasiurus /mp3]# touch blah
	touch: blah: Input/output error


This is /dev/sdc12 on /mp3 type ext2 (rw), 
Other partitions on the same drive are writable no problem. 

I can't umount it either:
	[lasiurus:/]$ sudo umount /mp3
	umount: /mp3: device is busy

Tho I don't know what else is using it, other than maybe SMB shares. 

What's causing this? 
How do I find out what's preventing the umount? 
Suggestions? I don't want to *gasp!* reboot.


Thanks, 

Andy