What's on the jukebox? Everything

PowerFile's Enterprise C200, priced from $4,999 to $6,499, can hold up to 940G of data and works with Windows and Unix platforms.

DISC's NSM series of DVD-RAM jukeboxes range from 1.34T to 6.49T of capacity and $5,800 to $13,200 in price.

DVD units give you quick access to archived data

A DVD has a lot to offer as a storage option. It's durable and long-lasting, good for long-term archiving, and it lets you find data quickly without rewinding tape media. You can write permanently, with no modification or alteration possible, or update continually.

The disks are inexpensive'in bulk buys they can cost as little at 58 cents a disk. Each holds a nominal 4.7G; a stack of about 200 DVDs represents one terabyte.

The problem is how to manage that stack, which is where the DVD jukebox comes in.

Like its namesake from the phonograph era, a DVD jukebox holds many disks, each in a separate slot. When a user selects a DVD, the disk moves to one or more drives within the unit for reading or writing.

A jukebox holds from hundreds of gigabytes to tens of terabytes of data. Units range from compact, under-the-desk models to cabinet sizes. You can rackmount some units with other system components, or simply connect them to networks through standard interfaces such as SCSI or Ethernet.

Some units offer the option of handling double-sided media, which raises disk capacity to 9.6G.

'DVD jukeboxes are especially important for large-scale archival applications,' said Wolfgang Schlichting, research director for removable storage with market researcher International Data Corp. of Framingham, Mass.

Magneto-optical (MO) disks, CD-ROMs and tape are the alternatives to DVD. Tape doesn't offer speedy random access and is comparatively fragile. CD-ROMs hold far less data per disk, only about 650M. MO disks are faster than DVDs but significantly more expensive; a single, 5.2G MO disk costs about $33, compared with DVD's retail price of about $3 or less per disk.

In addition, it might be possible for DVDs to last up to 100 years, depending on the quality of the media. 'Higher-quality DVDs cost more, but their durability is worth it, ' Schlichting said. And most DVD jukeboxes also handle CD-ROMs.

There are several varieties of DVD. A DVD-ROM (read-only memory), like a CD-ROM, is prerecorded. You cannot alter its contents.
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DVD-R disks can be recorded once, and then read many times. Typically, a disk's worth of data is stored on a hard drive and an image of the data created before it is burned onto the DVD. Of course, once a disk is full, it cannot be erased or re-recorded, so it acts just like a DVD-ROM.

DVD-RAM, DVD-RW and DVD+RW are all formats that allow incremental recording, erasing and re-recording.

DVD jukeboxes typically are accessed via a network, possibly as part of a system that includes such things as tape libraries and RAID systems. Often, more frequently accessed data is stored locally in a separate optional cache, which reduces the need to read the same DVD repeatedly.

This can ease the demands on the jukebox, and significantly improve performance for multiple users. Such DVD servers or virtual jukeboxes are becoming more common as adjuncts to DVD jukeboxes.

Special software is available to manage DVDs and their contents. For example, indexing software can keep track of the location of information, regardless of which single DVD it is on. Some software even lets you add descriptions to the contents, which can help when handling images.

Take a drive

Other software can make an entire DVD jukebox appear as a single drive to a network, simplifying access for users. Logging applications can keep track of who accesses what information when'important for secure or private information handling.

Most jukeboxes work with any operating system, provided the software supports the unit.

Besides current and projected storage needs, you also have to consider user access. If many users are accessing data simultaneously, you need a unit with a large number of drives to handle the demand.

If access is likely to be light, fewer drives are necessary, freeing up space for more DVDs. Never buy a single-drive jukebox: if the drive fails, you're left with an expensive DVD rack. If usage patterns indicate that many different DVDs are being accessed rapidly, the speed of the DVD-changing mechanism becomes more significant.

Edmund X. DeJesus of Norwood, Mass., writes about IT.

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