What options are you using to tar? If you are using "tar -xvf/-cvf", as far as I'm aware neither m-time or c-time should be modified. Perhaps adding "--atime-preserve" to your create command string "tar --atime-preserve -cvf"?
As far as a better way to accomplish the task. I would recommend using "rsync -av /source-dir /backup-device/backup-dir" to a usb device, and "rsync -av /backup-device/backup-dir /dest-dir". This will accomplish the same task, while increasing reliability + decreasing the amount of data that needs to be copied (only updates blocks which have changed, i.e., delta of changes). Rsync also uses a rolling md4 checksum algorithm which will give you the ability to verify the integrity of you files.
Hope this helps
Last edited by Forrest Coredump; 10-22-2009 at 11:12 AM.