IBM E16RMLL-I Implementation Guide - Page 80
Tape drives and sizing
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2.9 Tape drives and sizing In this section we discuss the calculations for estimating the size of a tape library to support a Tivoli Storage Manager solution. Similar calculations can be used to determine the total disk storage needed to support an environment. Most Tivoli Storage Manager designs incorporate tape and tape drives as the ultimate long-term storage locations for backups and archives. Therefore, it is important to understand the performance characteristics of tape drives and tapes when designing a Tivoli Storage Manager solution. When using tape storage pools, a Tivoli Storage Manager server should have access to no less than two drives. For architecture calculation purposes, assume only 80% of maximum, uncompressed throughput for a tape drive. Be prepared to do restores while other administrative operations are happening on the system or when drives are broken. Carefully consider card and bus throughput when attaching tape drives to systems. Most protocol/tape combinations can accommodate two or three tape drives per card. When using Fibre Channel/SAN attached tape drives and disks, do not mix disk and tape traffic on the same HBA. When planning for tape drive throughput and tape capacity, it is best to be conservative. Although drives can perform close to and better than their compressed rating, typically their performance is far less than this in reality. We use 80% of native uncompressed throughput ratings and 150% of native capacity ratings for theoretical calculations of drive throughput and tape capacity. Table 2-14 summarizes those calculations for some popular tape drives. Table 2-14 Tape device comparisons Tape drive Native speed (MBps) IBM LTO Gen 2 35 IBM LTO Gen 3 80 IBM 3590-E1A 14 IBM 3590-H1A 14 IBM 3592 40 STK T9840C 30 STK T9940C 30 Native capacity (GB) 200 400 40 60 300 40 200 Assumed speed (GB/HR) 98 224 39 39 112 84 84 Assumed capacity (GB) 300 600 60 90 450 60 300 50 IBM Tivoli Storage Manager Implementation Guide
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