I tried running my ext HD on CentOS; it mounted initially, but after unmounting it, it took several tries before it would mount again. I tailed /var/log on the tries and got this:

/* Tried mounting drive on CentOS. Successfully mounted and unmounted, then tried to mount again and failed. Took tail. Then took tail for every subsequent plug/unplug attempt, until HD successfully mounted. */

[root@localhost media]# tail /var/log/messages
Nov 27 16:16:17 localhost kernel:   Type:   Direct-Access                      ANSI SCSI revision: 00
Nov 27 16:16:17 localhost kernel: SCSI device sda: 312581808 512-byte hdwr sectors (160042 MB)
Nov 27 16:16:17 localhost kernel: sda: Write Protect is off
Nov 27 16:16:17 localhost kernel: sda: assuming drive cache: write through
Nov 27 16:16:17 localhost kernel: SCSI device sda: 312581808 512-byte hdwr sectors (160042 MB)
Nov 27 16:16:17 localhost kernel: sda: Write Protect is off
Nov 27 16:16:17 localhost kernel: sda: assuming drive cache: write through
Nov 27 16:16:17 localhost kernel:  sda: sda1
Nov 27 16:16:17 localhost kernel: sd 2:0:0:0: Attached scsi disk sda
Nov 27 16:16:17 localhost kernel: sd 2:0:0:0: Attached scsi generic sg0 type 0
[root@localhost media]# 

[root@localhost media]# tail /var/log/messages
Nov 27 16:16:17 localhost kernel: sd 2:0:0:0: Attached scsi generic sg0 type 0
Nov 27 16:16:34 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:16:34 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:16:34 localhost kernel: Info fld=0x0
Nov 27 16:16:49 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:16:49 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:16:49 localhost kernel: Info fld=0x0
Nov 27 16:17:00 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:17:00 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:17:00 localhost kernel: Info fld=0x0
[root@localhost media]# 
[root@localhost media]# tail /var/log/messages
Nov 27 16:16:34 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:16:34 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:16:34 localhost kernel: Info fld=0x0
Nov 27 16:16:49 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:16:49 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:16:49 localhost kernel: Info fld=0x0
Nov 27 16:17:00 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:17:00 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:17:00 localhost kernel: Info fld=0x0
Nov 27 16:18:22 localhost kernel: usb 4-5: USB disconnect, address 5
[root@localhost media]# 

[root@localhost media]# tail /var/log/messages
Nov 27 16:16:49 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:16:49 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:16:49 localhost kernel: Info fld=0x0
Nov 27 16:17:00 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:17:00 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:17:00 localhost kernel: Info fld=0x0
Nov 27 16:18:22 localhost kernel: usb 4-5: USB disconnect, address 5
Nov 27 16:19:01 localhost kernel: usb 4-5: new high speed USB device using ehci_hcd and address 6
Nov 27 16:19:01 localhost kernel: usb 4-5: configuration #1 chosen from 1 choice
Nov 27 16:19:01 localhost kernel: scsi3 : SCSI emulation for USB Mass Storage devices
[root@localhost media]# 

[root@localhost media]# tail /var/log/messages
Nov 27 16:19:14 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:19:14 localhost kernel: Info fld=0x0
Nov 27 16:19:20 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:19:20 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:19:20 localhost kernel: Info fld=0x0
Nov 27 16:19:26 localhost kernel: sda: Current: sense key: No Sense
Nov 27 16:19:26 localhost kernel:     Additional sense: No additional sense information
Nov 27 16:19:26 localhost kernel: Info fld=0x0
Nov 27 16:19:27 localhost kernel: SELinux: initialized (dev sda1, type vfat), uses genfs_contexts
Nov 27 16:19:27 localhost hald: mounted /dev/sda1 on behalf of uid 500
[root@localhost media]#

But since it did mount, and I know I can access the drive in an emergency, I'm going to go ahead and reinstall Dapper and upgrade it from there to Feisty (since I'm lacking a Feisty CD, and I remember seeing that Dapper could upgrade directly to Feisty).