Yes, it's an external case for a hard disk, and, yes, it costs ÂŁ350 without a single drive fitted, but we're still really excited about this product.

To understand why, you have to understand the problems it's here to solve...

The life of a hard disk

A regular external hard disk has a finite capacity and no methods of its own to guard against data loss through drive failure. When it's full, you have to buy a new drive with a higher capacity and copy the data across, or, if it crashes, buy another and hope that your backup regime will have saved your files.

And when you do replace the drive, you have to decide whether to shell out for the highest capacity drives available or go for one a size or two down and risk running into the same problems a few months down the line.

RAID enclosures solve some of these problems. Here, you slot in matching drives and, depending on how you configure the system, you'll have so-called data redundancy; if one drive fails, you can simply pop it out, slot in a replacement, and the RAID box will automatically rebuild the set.

The problem here is that RAID works best if you use identical drives in each bay, and though you could in theory choose to include some higher capacity drives, the final pool of storage you have is defined by the lowest-capacity drive on the system.

Brave new world

Welcome, then, to a new world of storage with Drobo. It has four drive bays and you can slot any capacity and type of drive into any of the four bays; the Drobo automatically gives you as much capacity as possible.

It doesn't use any of the usual RAID flavours; instead, a proprietary data management system moves information around the drives, and a system of traffic lights lets you know the status of your data; it's managed so that if one drive fails, you're still safe - just pop in a replacement.

Set-up is a doddle - a big, simply illustrated sheet in the box takes you through the three-step process. There are no drivers - modern Macs and PCs just see it as a big external hard disk - and a crib sheet fixed to the reverse of the magnetically-attached front face reminds you what the status lights mean.