IBM E16RMLL-I Implementation Guide - Page 82
Tape devices, Tape libraries, Number of tape drives
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Total tape volumes required Assume 10% growth in first year Option 68 75 2.9.1 Tape devices Tape drives come in all sizes, including, but not limited to, DLT, SDLT, LTO, 3590, and other device types. Each type of drive has a different data capacity, performance, cost, and reliability characteristics. Although data capacity and cost per megabyte stored are important, reliability is much more important. Having saved money buying tapes is small consolation when you are unable to restore your customer billing database due to a tape error. In general, tape drives where the tape touches the read/write heads, such as 4 mm and 8 mm, tend to be less reliable (and slower) than tape drives where the tape does not touch the read/write heads, such as 3580 and 3590. If you do implement drives that touch the read/write heads, plan to replace the tapes at regular intervals. 2.9.2 Tape libraries Tivoli Storage Manager was designed with automation in mind, specifically for automated tape libraries. The best and easiest way to run a Tivoli Storage Manager library is to keep all on-site data in the library so that tapes can be mounted automatically when needed for restores, backups, reclamation, and other Tivoli Storage Manager administration processes. 2.9.3 Number of tape drives In attempting to reduce costs, some Tivoli Storage Manager customers might consider purchasing only one or at most two tape drives. Although the Tivoli Storage Manager could be configured with only one drive (or with a library containing one drive), we do not consider this to be a production-level solution and do not recommend it. A single drive solution cannot make additional data copies (for disaster recovery purposes) or perform space reclamation without considerable manual effort and additional disk resources. Any Tivoli Storage Manager server for production use should have a library with two or more tape drives. Here are some business reasons for selecting a multiple-drive solution: To avoid a single point of failure To avoid interruptions to automated backup processing (reclamation, backup stgpool, migration contention) 52 IBM Tivoli Storage Manager Implementation Guide