Off Site Backup: Removable hard-drive racks or external USB hard-drives?

[Andy <andy@besy.co.uk>]

Hello List,

I am building a backup server using Debian and BackupPC, and would like
to have an off-site backup rotated weekly.

I wonder if I might ask the list's opinion about which hardware I should
use to store the off-site backups on?

My tar archive is too large for tape (~300GB) so I have been considering
either:

- removable hard drive racks with SATA disks enclosed in a caddy
- external hard drives connected through a USB2 or firewire interface

The "SATA linux software status report"[1] indicates that hot-plug is
unsupported for SATA disks.

Q) Is still the case where the disk is connected through a removable
hard drive rack claiming to support hot-plug?

Q) Is hot-plug supported for external hard disks connected through a
USB2 or firewire interface?

My script can umount and mount as necessary, but I would like to avoid 
reboots if possible.

Q) Do you foresee any problems configuring LVM or software RAID on top
of removable or external disks?

Thanks for your help, Andy

[1] http://linux.yyz.us/sata/software-status.html