In the past, WORM usually meant optical media from vendors such as Plasmon or Sony. But now, Sony is also selling WORM-capable AIT-2 and AIT-3 tape drives and media, which it is shipping to tape library vendors Spectra Logic, Qualstar, and Overland Data.

The net effect could be to drive down archiving costs, says John Woelbern, Sony director of OEM tape sales and marketing. Certainly, the cost per gigabyte of tape is much better than optical. Whereas an AIT-3 tape offers 100GB of native capacity for under $100 per cartridge, (<= $1/GB), optical media costs between $15 to $20/GB, and offers less capacity per disk.

Beyond cost per gigabyte considerations, says Sharon Isaacson, product manager at Spectra Logic, tape WORM enables customers to avoid the purchase of separate tape and optical libraries. "They can save themselves quite a bit of money that way," Isaacson says.

The only other tape manufacturer to offer a WORM option is StorageTek, with its VolSafe technology for its 9840 and now 9940 drives. According to Jana Tompkins, product marketing manager, demand for VolSafe media is driven largely by StorageTek's financ...

Many AIT-2 or AIT-3 drives on the market are already WORM-capable, and recognize the media as WORM from the cartridge's firmware. But whether archival applications will work with AIT tape WORM is another story. So far, only a few ISVs have certified their applications for AIT WORM, including BakBone Software, Dantz, and newcomer XenData, with its Archive Series Software, an HSM-like solution that supports archival across disk and AIT WORM tape.

But once application support falls into place, what reason would you have to buy an optical WORM solution? For one, access time, says Phil Storey, XenData CEO, but who was also one of the original founders of Plasmon. Tape can write data much faster than optical disk, but access times are on average 37 seconds to optical's 10 seconds. XenData circumvents tape's poor access speeds by packaging its software with a front-end disk cache.

So, how long do you need the data around for?, asks Andrew Richards, VP of development and marketing at Plasmon. If you only need to keep data for two to three years, then tape WORM is probably good enough, he says, but if you need to keep it for longer, "tape comes up short." Despite vendor claims, "my real- world experience says that tape's longevity is not the 30 to 40 years represented by the industry."