Yes, it's an external case for a hard disk, and, yes, it costs £350 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.

Hot-swappable

If one of the lights next to a particular drive goes orange, it's 85% full and should be replaced with a higher capacity model, solid red means 95% full, and blinking red means the drive has failed. If they're anything other than green, you can - while the drive is still being accessed - pop the drive out and replace it; the lights will blink as your data is rebuilt.

This hot-swappable, organic-growth system means that the unit has essentially unlimited storage, and you can happily buy 750GB or 500GB drives to get you started rather than punishing your credit card with 1TB units.

We threw in a couple of 1TB Western Digital Green Power drives and some older 750GB and 500GB ones, and it worked just fine. Since it can be formatted as HFS+, it's supported by Time Machine, too.

Pros and cons

But it's not perfect. Performance isn't stellar - using it as a repository for television recordings was occasionally frustrating, thanks to sporadic drop-outs - and there's only a single USB port at the rear. Its fan can get noisy during rebuilding, too.

It's also annoying how the drive reports its capacity to the host computer, although a recent firmware upgrade has helped mitigate this. And if things do go catastrophically wrong, we'd have more confidence in an independent company's ability to recreate data from a vanilla RAID setup than from Data Robotics' data schemes.

But even with these niggles, it's still a fantastic data storage solution, and we want one.