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Tape libraries automate backup

Ezine

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A library, in contrast, has more than one drive. Libraries range in size from small footprints up to room-size models comprised of chained-together libraries serving an entire enterprise. Libraries usually have express cartridge access to load an individual tape or groups of tapes. Larger libraries have bar code readers to inventory and keep track of tapes, magazine-style express slots and a host of other features.


Scoping out tape library vendors

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COMPANY AUTOLOADER LIBRARY
FOR MIDRANGE
LARGE LIBRARY
FOR ENTERPRISE
ADIC
ATL
Benchmark NO NO
Exabyte
HP
IBM
Overland Data NO
Sony NO NO
StorageTek
Source: Evaluator Group; * Denotes 2U rackmount
A word of caution about large libraries that read bar-coded tapes: All bar code readers are not created equal. You may get errors reading bar codes when mixing different automation vendors. Worse yet, you may have errors reading the particular bar code already on your large library of tapes. Send the vendor some of your standard bar code labels. Have them test and confirm that their model can read your labels.

Library vendors keep increasing system densities to decrease footprint. Another trend in library design is the use of auxiliary memory on cartridges for faster operation and more intelligent diagnostics. Libraries typically have a life of five to seven years and the tape drive technology may be upgraded during this time. All major computing platform environments are supported.

Libraries allow two or more drives to access a large number of cartridges. The transfer rate for the library is essentially equal to the transfer rate for a single drive multiplied by the number of drives, minus a little overhead, which all adds up to transfer rates of over a terabyte of data per hour. New formats and migration roadmaps associated with tape formats like LTO, S-AIT and SDLT, along with faster robotics, are raising the bar on capacities and transfer rates. Libraries are denser, smaller and faster than anyone thought possible a few years ago.

When sizing automation to an application, consider the ratio of drives to cartridges. For capacity, fewer drives are used. For transfer speed, more drives are used. Make sure that you have the actual transfer rate (less overhead) needed to meet your business recovery time objective.

Use TCO analysis to evaluate libraries
Vendors traditionally sold libraries via relationships, strong product features and functions. Users looked at TCO as the cost of hardware, software, maintenance contracts, power use and personnel to install, operate, manage and maintain an IT system - the technology TCO. As technology costs continue to drop and personnel and business costs continue to rise, business issues have assumed more significance and can no longer be left out of the TCO assessment.

Libraries should be selected based on how well they support the business TCO. The business TCO addresses the potential dollar cost/benefit to the user and business, showing how well the proposed library improves availability, performance and recovery cost impacts. Business costs have the greatest impact on a company's recovery from an outage and must be part of the TCO evaluation (see http://www.evaluatorgroup.com for a free white paper detailing TCO calculation).

You won't want to send a library back once installed, so include an on-site service contract in your calculations. Make sure you get the service level you need. It's a good idea to have a spare tape drive on hand: Will vendors provide a spare drive? Media cost can be the largest expense in large systems: Is there a special media purchase price bundle with a new library? Tapes can be reused, but need to be retired when they have been used for specified passes, or begin to show a rise in soft errors reported by the backup software. Include that in your TCO.

Choosing a tape format
There are more choices today for tape drives than ever before. There is no perfect format for all of your applications - you should consider the best choices for work groups, midrange systems, enterprise systems and specialized applications on their own merits.

This was first published in June 2002

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