It's considered a safe practice to make incremental backups to an external hard drive in case disaster strikes. The same goes for road warriors, many of whom already make it a habit of backing up regularly on the go. However, who's to guarantee the backup drive won't fail on you when you most need it? The safest way to go is a RAID1, but there isn't any portable version yet... until now.
ACARD ARS-2212 Mirror Smart Mini can accommodate two 2.5" SATA drives that are bridged to a hardware RAID 1 chipset, free CPU loading and providing seamless data mirroring. You can also set it to normal mode so the system sees the drives as two external disks. The ARS-2212 - measuring at 163 x 16 x 163mm - isn't bad at all only if USB 2.0 can provide more power so we can all carry this around leaving the AC adapter at home.