Disk vs tape?

For the last 50 years, since the earliest days of the computer age and right after the demise of paper tape and punch cards, the question has been repeatedly asked: hard disk or tape - which is the best backup and storage medium?

Back in the day, the competition lay between huge open-reel tape drives - looking much like the massive film reels of the projector era - and equally large removable hard drives. Both media were managed by a staff complement that often worked the night shift simply to load the previous day's activities onto these giant repositories, via refrigerator-sized drives, to complete the backup process.

There were organisations that put their faith in tape and others who preferred the hard drive option. Each had a core of committed evangelists who would swear by 'their' media's benefits, while pointing out the shortcomings of the opposition's choice.

It wasn't until the mid-80s, when the (then) Exabyte Corporation developed the 8mm tape drive, that tape took the lead in the media war. This innovative cartridge held 2.3GB of data. It was much like an audiocassette tape in size and appearance. The technology represented a quantum leap ahead in the technology race. Suddenly tape was in vogue.

Exabyte's groundbreaking backup cartridges and attendant tape library technology heralded the concept of unattended backup - called 'lights out' backup then - which made the night shift redundant and cut the emphasis on (costly) human resources in the backup process.

With tape drives steadily increasing in capacity, thanks to data compression and advances in recording density, they soon outpaced disk as the cheaper backup option. And tape's prices began - and continued - to fall, entrenching its position as the backup medium of choice well into the next decade.

However, in the late 90s, hard disk technology began a renaissance as a result of stoic support from a number of vendors. Gradually, the oversized removable hard disks were replaced by smaller and more compact fixed drive units. Over the years, the size of the drives reduced further and their capacity increased manifold.

While prices have been falling steadily to this day, disk technology has also taken a series of forward steps with easily accessed, miniature high capacity drives now available, presenting end-users with an alternative comparable in terms of performance and price to tape. Is hard disk technology edging ahead once again in 2010?

It's hard to tell. Each technology has its champions and detractors. For example, tape is seen as an inflexible and slow solution by disk protagonists - who underline their systems' low cost, speed of operation with the ability to add features such as data de-duplication and single instance storage on demand.

Steve Hammond, senior VP at Data Protection Solutions, a hard disk advocate, says: “If you're trying to pick the right backup solution and your business couldn't survive a day or two without quick access to data, you need to ask: how quickly can this solution get my critical data backup and running if I suffer a failure?

“With disk storage the answer is, pretty quick. Unlike tape, which typically stores data in a linear fashion, meaning you have to start at the beginning and run through it until you find what you're looking for. Disk storage is more like a mirror, reflecting every aspect of your system at once,” he says.

Each technology has its champions and detractors.

John Hope-Bailie is technical director of Demand Data.

Tape supporters, on the other hand, point to the many inherent benefits of tape, in particular its portability. A vast quantity of data may be removed from the production site to secure storage or a DR site by the relatively simple (albeit repetitively tedious) process of manually transporting a canister of tape cartridges from A to B.

The effective bandwidth cost of this mundane method can simply not be met in any other way. In addition, the audit trail presented by tape media is a natural advantage.

Tape system scalability is also a major factor. With the latest tape capacities exceeding 1TB per cartridge and throughputs of around 500GB per hour, even the performance of a single tape drive is impressive. But by configuring multiple tape drives in a library, substantial throughputs can be achieved, often far exceeding the performance of more expensive disk systems.

Expanding the overall capacity, a tape-based system is also easier. Instead of the capital outlay of installing more hard drives, all that's needed are additional tape cartridges.

In addition, the 'green lobbyists' have been quick to board the tape bandwagon, revealing that tape drives tend to consume significantly less energy than hard drives, helping to reduce the corporate carbon footprint of the user.

So, is there a conclusive answer to the 'tape vs disk' question?

In today's world, tape and disk both have their respective positions and virtues. It's possible, therefore - depending on a company's needs - that some combination is best.

The most likely answer is embodied in D2D2T (disk-to-disk-to-tape) systems. These hybrids make the best of both technologies, optimising the access speed and convenience of hard disk drives with the scalability and portability of tape storage for offsite backups and deep archiving - and for additional peace of mind.