I have a usb drive to which I wish to write. Format is ext3. Can read, delete, but cannot write. Following is terminal output:

root@Aidan:/media/USB shared# mount
/dev/mapper/vg0-root on / type ext3 (rw,errors=remount-ro)
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
/dev/mapper/vg0-home on /home type ext3 (rw)
/dev/mapper/vg0-opt on /opt type ext3 (rw)
/dev/mapper/vg0-tmp on /tmp type ext3 (rw)
/dev/mapper/vg0-usr on /usr type ext3 (rw)
/dev/mapper/vg0-var on /var type ext3 (rw)
none on /sys/bus/usb/drivers type usbfs (rw,devgid=119,devmode=664)
rpc_pipefs on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
nfsd on /proc/fs/nfsd type nfsd (rw)
vmware-vmblock on /var/run/vmblock-fuse type fuse.vmware-vmblock (rw,nosuid,nodev,default_permissions,allow_other)
/dev/sdf on /media/ARCHOS type vfat (rw,nosuid,nodev,uhelper=hal,uid=1000,utf8,shortname=mixed,flush)
/dev/sde1 on /media/USB shared type ext3 (rw,nosuid,nodev,uhelper=hal)
root@Aidan:/media/USB shared# mkdir Archos
mkdir: cannot create directory `Archos': Input/output error
root@Aidan:/media/USB shared#


What did I do wrong?

This looks like the drive might be faulty. Could you try it on another machine to try and confirm? Or try another drive on this machine?

yep, it looks like a bad cluster that the drive tries to write upon and fails. Check the drive for bad sectors e.g. using badblocks command

Yes, the drive had a large number of bad blocks - not surprising, considering its age. The following command cleaned them up:

root@Aidan:/home/aidan# fsck.ext3 -vy /dev/sde1

Now I need to locate a cheap (no cost!) replacement drive.

Many thanks for your guidance.

well, if you're short of cash at the moment, you still can try to use the drive. First, backup all the data that you find to be critical for you, of course. Then 'label' the bad sectors as unusable. Use 'e2fsck -c' for that. You can read more on smartmontools how to's.
This is by no means a permanent solution, but if this is a flash drive you use just for sharing some data you're not afraid to lose occasionally, it might still be used for a pretty long period of time. Anyways I would get a new drive on the first occasion since they're cheap as peanut nowadays.