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Once upon a time, you could find tape drives everywhere. Even home offices used DAT, QIC and other small tape cartridge formats to do backups. In the days when having a hard disk as large as 500MB seriously impressed people, tape was pretty much the only economical way to make a copy of your data.

So what went wrong for tape – or more accurately, what changed? Because tape has not disappeared altogether, as some people seem to imagine.

It is still around and in some areas it is doing better than ever – especially when used in combination with hard disk, either in a combined backup appliance with deduplication capabilities or as tiers within an archive.

Repeated patterns

A big part of the change in the storage landscape was the huge advances in hard-disk technology and capacity, which for years were not accompanied by equivalent advances in tape technology.

Bob Plumridge, chairman of storage industry group SNIA Europe, also points to the development of deduplication. This technology looks for repeated patterns in data and stores or transmits each pattern only once, with subsequent copies replaced by a pointer.

Depending on the kind of data being handled, commercial users have reported deduplication giving an effective compression ratio as high as 20:1 or even 50:1. It varies widely simply because some datasets contain more duplication than others – for example, virtual machines created from the same template will be almost identical.

Fortuitously, deduplication reached the market at about the same time as high-capacity and low-cost hard disks using the new SATA interface, which significantly simplified their cabling.

SATA drives were largely aimed at the consumer market, but it was quickly realised that with the right packaging (advanced RAID) and deduplication, they could equally well provide huge amounts of relatively slow, but also relatively cheap, enterprise storage.

"With the advent of deduplication we are seeing lots more backup to disk. Then at some point they might move stuff off to tape, where a few years ago it would have been backup straight to tape," says Plumridge.

Single file

Another part of the change was in the way people expected to use backups. These used to be designed to get the entire system back if it failed, but increasingly people wanted to recover individual files that had been accidentally overwritten or deleted.

This was a pain with a sequential medium such as tape, even if the backup was in a mountable format, but it was comparatively easy to do with random-access disk.

There was also the growing realisation that each type of storage has its strengths, and that vendors needed to focus on those – in effect, that they needed to complement each other, not compete. It also meant they needed to be managed together, which spurred the development of software and hardware appliances that could provide that coordinating layer.

So while tape has largely disappeared from roles where disk is better suited, such as fast or random access, handling multiple backup jobs in parallel, start-stop usage and deduplication, it has seen something of a comeback in areas where it has unique strengths, such as streaming speed, low-cost media and long-term storage.

In addition, the development of tape technology has accelerated since the turn of the millennium, so those strengths once again include high data densities, with the latest LTO-6 generation able to hold 6TB or more of compressed data per cartridge.

Handle with care

Steve Mackey is vice-president international at Spectra Logic, one of the very few old-school tape suppliers to have survived and prospered. "I think everyone is used to the idea now that tape has its use cases,” he says.

“It is highly performant and scalable, it needs very low power consumption too, and adding a tier of disk overcomes the main disadvantage of tape, which is latency," he says.

Mackey acknowledges that 1990s tape technology had its flaws. Tape failures were not uncommon, so that some sysadmins swore off tape altogether and were only too happy to see disk-to-disk backup become practical.

But he argues that as much as anything that was down to it being used the wrong way – even though for the right reasons.

"The majority of users' bad experiences with tape as backup from 10 or more years ago was because people weren't handling the media especially well," he says.

"Once it is outside the library, media is prone to mishandling – and operators were unlikely to tell anyone if they dropped a cartridge. Plus it might be moved off-site or stored in a room that wasn't temperature controlled.

"In addition, media was often over-used if there wasn't a good tape rotation plan in place. Backup is a high-pressure environment, so people took less care over the media than archive owners would."

Two key things have changed, he says. First, with disk arrays taking over front-end backup duties (and now the cloud taking over at the low end), modern tape cartridges mostly live in automated libraries which they rarely leave.

Low-end tape drives have all but disappeared, leaving the market dominated by the high-end formats. Primarily this means the LTO standard, with smaller market shares held by Oracle-StorageTek's T1000 and IBM's TS series.

"The reliability of tape has improved 700 per cent in the last 10 years or so”

Mackey points at a second factor. "The reliability of tape has improved 700 per cent in the last 10 years or so,” he says.

“The fundamental reliability of the tape storage medium is higher than that of Fibre Channel disk, which is the most reliable disk medium today. Tape actually has a lower bit error rate than disk.”

"It is partly the focus on LTO and on customer satisfaction, but the vendors also built in media lifecycle management and data integrity verification, which checks the health of the media periodically.

"LTO performance and capacities are also evolving very well, and the cost per terabyte improves with each generation. LTO-6 came out in December 2012 and was one of the fastest new technology take-ups in years. Customer confidence has improved dramatically, partly because the experience with LTO-5 was so good.”

Mackey adds that a hard disk on its own can fail, so we put them in arrays and we do backups.

“It is the same with tape. In big content archives you will always have data protection, probably including at least one duplicate. The most valuable data will have two copies in different locations, similar to disk mirroring," he says.

Partnered with disk

As tape has come to be accepted as complementary to disk, so the need to manage the two and make them play well together has grown.

That is accentuated by the way that almost exponential storage growth has lead to the evolution of data protection silos, according to Frank Reichart, senior director product marketing for storage at Fujitsu.

"The problem is that data growth is faster than the growth of disk capacity," he says.

One consequence of this is that data protection has evolved into disparate islands, he adds, as the various server and application teams fight valiantly to keep up.

In addition, certain server architecures (x86, Unix, mainframes) and applications support only certain backup options and this too leads to the development of silos.

All this in turn has brought opportunity and advantage for the developers and users of backup appliances, whether disk to disk or disk to disk to tape. These virtualise the physical target disk or tape systems and emulate several logical backup devices, typically multiple virtual tape libraries.

Control centre

The appliance can therefore provide a single target for a variety of backup servers and software, as well as being a centralised point of control for all of an organisation's backup needs.

This ability to cover multiple heterogeneous systems with a single backup platform is a big advantage of the appliance approach, argues Mike Coney, CEO of all-in-one backup developer Unitrends.

The hardware that underlies backup, archiving and disaster recovery is much the same. With the right software the same appliance can offer all these services through a single management interface.

"There has been a trend to say tape is dead, but as you start building silos, now you need combined management " says Reichart.

He adds that as well as offering the advantages of both disk deduplication and tape, backup appliances such as Fujitsu's Eternus CS can also process data and build a backup without overloading either the backup or application servers.

Once the data has been received, the appliance takes care of all further data management. Furthermore it can act as a target system for archiving data due to its NAS functionality

Future developments are backup appliances that also act as cloud gateways, enabling storage professionals to add external storage as an additional option for backups and archives. ®

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