Why buy a tape autoloader if you can do the job better with a disk-based storage array? That's the question posed by Diamond Lauffin, a veteran of the storage industry who is now senior executive VP at disk backup developer Nexsan.

There have always been arguments why tape would stay around, such as the ability to archive cheaply or to take cartridges out for off-site storage, but all of them eventually come down to cost - and that is no longer valid, says Lauffin, who acquired his unusual name during a stint as a professional musician.

He lists a range of organisations which he claims have enlisted disk not merely to speed up backup to tape, but to replace it altogether, including Hotmail, Cisco, JPL and UPS. "UPS evaluated tape versus disk and found it could archive up to one year on disk for equal cost," Lauffin says.

"We've been debating the tape question in the US for three years - the debate is over now and we have hundreds of companies going to disk-based backup every month, whether it's to Nexsan, Quantum, NetApp, StorageTek or whoever. "Implementing a disk-based backup solution is no different from implementing tape-based backup.

Tape is no longer cheaper than disk - tape is less money, yes, but that's not a fair comparison." He says that, by the time costs such as management and the necessary redundancy have been included, the falling cost of hard disk capacity means that the two are now on a par. And he argues that, far from reversing this trend, "the 1TB tape will be the tape industry's demise, not its saviour. "Most end users would say they are interested in 1TB tape, but the question is are you compressing your data? In most cases the answer is yes, so you could be putting 3TB onto each tape - that's good.

The next question is are you going to put 3TB on a single point of failure? "All the arguments for tape have been cost-based. However, the backup/restore process has a 10 per cent to 15 per cent failure rate, so most users will make a second copy of each tape, as they have done for years, and as soon as you make two tapes, tape is more expensive than disk." He adds that, although many of the arguments made for disk backup so far have been speed-based, "Our first disk backup systems never went in because of speed, they went in because of reliability.

Those users wanted RAID-5 and they wanted to monitor that their data really was available." That availability is a key element of Nexsan's approach to disk-based backup. Lauffin says that with path-redirect technology, information requests can automatically be rerouted to the Nexsan device, allowing data to be reacquired in less than an hour. "The most active topic is reacquire versus restore," he adds. "The primary issue is slightly faster restore, that's OK but it's not all we can do. We are a proponent of replicas and of backing up those replicas with versioning, but also to disk - we believe in multi-staging." To make disk backup affordable, Nexsan and its rivals have all turned to ATA and Serial-ATA hard drives, but Lauffin is keen to stress that these are not the same as the drives used in desktop PCs. "The disk manufacturers now have ATA and SATA drives rated for 24x7 use, usually with fluid motors and three-year warranties, so we use those higher-spec drives - it's like Skoda and VW sharing the same engine, chassis and production line, but with different bodywork," he says. "For example the new Hitachi 250GB ATA drive is identical to its SCSI and Fibre drives, but cheaper. We have drives in Philips digital CCTV systems running 24x7 and they are failing no more than SCSI. Video security was the first industry to adopt tape replacement wholesale - disk has advantages of no videotape management and better reliability, usability and flexibility." Far from being a handicap, the desktop heritage of ATA actually brings benefits to the backup market.

In particular, it helps Lauffin address the question of just how much extra all those spinning disks add to increasingly expensive electricity bills - a key cost in areas such as California. "We have electronic mount and load - it provides hierarchies of power saving, for example we can spin the disks slower and unload the heads, or selectively spin down RAID sets. This is stuff that ATA drives were designed to do, whereas Fibre drives are not," he says. "We are not advocating that tape will disappear overnight, but as companies move forward and have more budget and are educated, they are adopting disk - disk is a better option than tape in every area."