Western Digital has beefed up its My Book Pro line of external hard drives with a RAID-equipped model that packs in two HDDs to yield a whopping terabyte of unformatted storage capacity.

The My Book Pro Edition II sports a trio of Firewire ports - one 400Mbps connector and two 800Mbps ports - and a USB connector of the kind you usually see on the back of printers.

Hooked up to a host computer, data transfered to the drive can be mirrored across the two hard drives in case one of them fails. That cuts the capacity to 500GB, but provides better data security than the alternative, RAID 0 setting, which sets the drive up as a single 1TB data store.

WD said the product was "user-serviceable" - so you can pull out the drives in the near future and replace them with higher-capacity units, all in the knowledge that your three-year warranty still applies.

WD is bundling EMC's Retrospect Express version 7.5 backup and system recovery software with the My Book Pro Edition II. Available in the US now, the external drive costs $549. ®