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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