e network administrator sets a backup schedule and simply changes the magazine once per week or month. Without one of these devices, you have to manually swap tapes during backups.
Our roundup includes a hodgepodge of units that range from Seagate's internal 4586 NP ($2471) to ADIC's Scalar 458 2000XT ($50,995 as tested), which is a DLT-based tape library housed in a waist-high cabinet that can back up 4 TB of data. The DLT libraries offer the most capacity per cartridge. These cartridges provide an uncompressed capacity of about 10 GB, compared to about 4 GB for the 4-mm tape drives and about 5 GB for the 8-mm helical-scan tape drives. The higher-end tape auto-loaders ha
ve multiple drives; this provides such benefits as concurrent operations, fault tolerance, and increased throughput.
To evaluate these products, we ran tests (see the article "Test Specs") that measure how fast each tape library could back up and restore 920 MB of data spread out through a file-directory tree. We also checked the tape libraries for usability and features, and then we picked winners in each technology category. We didn't examine server-backup software, but we list what applications the tape libraries support in the features table.
4-mm (DAT) Libraries
The seven 4-mm drives that we tested (sometimes called DAT because of Hitachi's original DAT format) are standardizing on the DDS-2 (digital data storage) format for the tiny tape cartridges. This format was developed to let data transfers occur in SCSI-2 burst mode. DDS-2 doubles the density of the previous DDS format for 8 GB of storage on a 120-meter tape, but it maintains full DDS functionality and ensures full ba
ckward compatibility to the DDS and DAT 4-mm tape formats.
Four of the higher-end DAT tape li-braries that we tested are in the $8000 to $11,000 price range--Aiwa's AL-D220 AutoLoader ($7995), ADIC's VLS (Virtual Library System) 4mm ($9295), the DATa-ray 32 from Storage Solutions, Inc. (SSI; $9995), and the Exabyte 218 4mm Tape Library ($11,500)--and have multiple tape drives for reading multiple cartridges. This multitasking capability is important when you consider that, in theory, SSI's DATa-ray 32 could significantly reduce backup times if all five DAT drives were moving data at the same time. The Aiwa, ADIC, and Exabyte products have two tape drives each.
The Aiwa AL-D220 supports 17 4-mm tape cartridges in an upright chassis for 136 GB of data with 2:1 data compression enabled. The Exabyte 218 4mm Tape Library is a stand-alone unit that supports 19 4-mm cartridges for 152 GB of compressed storage. As its name implies, the SSI DATa-ray 32 can store 40 GB of data and offers excellent expandabili
ty, thanks to its stackable design. ADIC's VLS 4mm is a desktop device that can hold 15 cartridges for 120 GB of data; a robotic cartridge handler slides on a track in front of the tape magazine to enable you to move the cartridges back and forth to the tape drives.
The three remaining 4-mm tape libraries are single-drive units that provide backup on a much smaller scale. Hewlett-Packard's SureStore 12000e ($3510), Micro Design International's SCSI Express 2000DC ($3595), and Seagate's 4586 NP are no bigger than a shoebox. The Seagate 4586 NP (formerly a Conner product) is so small that it fits inside a PC, but it still backs up 96 GB of data.
DLT and 8-mm Libraries
DLT is gaining market share in the LAN segment of the industry because it offers higher capacities and is faster than the 4- and 8-mm tape libraries. In contrast to helical-scan technologies, DLT drives' serpentine recording method places data in longitudinal tracks. As a result, the drives can read and record multip
le channels of data simultaneously. The tapes also supposedly have a 30-year shelf life, which matches that of magneto-optical storage.
Quantum's DLT 2500XT ($4995) is a single-drive tape library with a five-cartridge magazine that you slide into the front panel for 150 GB of backup with 2:1 compression. It's the lowest-priced DLT tape library we tested. Overland Data's DLT Library Xpress/LXB 2210 ($15,495) offers 300 GB of backup in a rack-mountable case with a front-loading tape magazine. ADIC's Scalar 458 2000XT is the big daddy of all the tape libraries; it supports about 4 TB of data when its 48 cartridge bays are maxed out.
The Exabyte 210 8mm Tape Library ($13,325) and the Qualstar TLS-4220 ($12,500) have dual 8-mm Exabyte-manufactured tape drives. The Exabyte 210 8mm can hold 11 cartridges in its snap-in magazine, for 154 GB of compressed data storage. Qualstar's TLS-4220 supports two 10-cartridge magazines, for 280 GB of stored data.
Contributors
Jim Kane, Project Manager/NSTL
Dorothy Hudson, Project Manager/NSTL
John McDonough, Technical Writer/NSTL
Maggi Bender, Technical Analyst/NSTL
Susan Colwell, Technical Editor/BYTE
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12 Tape Libraries for Network Backup
