IBM E16RMLL-I Implementation Guide - Page 84
Backup tapes, Backup tape calculation
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requirements, and therefore, the calculation may not be linear. In any case, keep in mind that it is best to assume a middle case/worst case scenario so that you do not run out of tapes. Backup tapes To calculate the number of on-site tape volumes required for backup operations, carry out the following calculations: 1. If this is a sequential storage pool (tape device), multiply the primary storage pool size by the number of backup versions from Table 2-5 on page 26 to give versions pool size. 2. Add the sum of all Total storage used fields for each client from Table 2-1 on page 18 to the versions pool size, giving tape pool size. 3. Divide the tape pool size by the device capacity to find the number of tape cartridges required. 4. Add 50% to cater to tapes that are in filling status to give the total cartridges required for on-site tapes. 5. If using collocation, normally there should be at least as many tape cartridges as there are clients. Consider tape native capacity as a rounding factor. We do not use the compressed capacity of the tape here because we factored the client compression rate into the calculation of the storage pool size. If data is compressed at the client, it will not receive any benefit from hardware compression done by the tape drive. Backup tape calculation To calculate: 1. If the primary storage pool is 254 GB, and the number of versions kept is 7, then multiplying 1.04 * 7 gives a 1778 GB versions pool size. 2. If the all the clients are using 1200 and 400 GB, then 1200 + 400 + 1778 equals 3378 GB. 3. If the tape device has a capacity of 400 GB, then dividing 1938 by 400 gives 9 cartridges required to store all the data. 4. 5 * 1.5 gives 14 total cartridges required for on-site tapes. 5. If we use collocation for the database servers, since there 4 database servers and 20 file servers, we have enough tape volumes. 54 IBM Tivoli Storage Manager Implementation Guide
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