IBM E16RMLL-I Implementation Guide - Page 85
Archive tapes, Image backup tapes, Image backup tape calculation
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Archive tapes For archive tapes: 1. Using Table 2-1 on page 18, multiply the GB copied per archive by (1 - the data compression rate), giving transferred archive data. 2. For each client, multiply the transferred archive data by the number of archives kept in a year times the yearly retention ratio (that is, desired monthly retention/12 months), and sum up, giving total archive data. 3. Divide the total archive data by the native tape capacity, giving the total number of tapes required. Archive tape calculation To calculate: 1. The clients in our table have 200 GB and 80 GB of archive data. The compression ratios are 0.5 and 0.66. This equals 200 *(0.5) and 80 * (0.34), which equals 100 and 27.2 GB. 2. The number of archives kept are 12 and 12. The yearly retention ratios are 12/12 and 12/12. This equals 100*12* 1 + 27.2*12*1 = 1526.4 GB. 3. If the tape device has a capacity of 400 GB, then dividing 1526.4 GB by 400 gives 4 cartridges required to store all archive data. Image backup tapes Image requirements are calculated on total allocated file system space. For the sake of simplicity, we are not considering any compression rating (you can use the compression ratio for the client on the sum of file systems), and therefore the number is already overestimated without any need for extra tapes: 1. Consider all client file spaces eligible for image backup. Sum them all, giving transferred image size per client. 2. Using Table 2-1 on page 18, multiply the number of image backups by transferred image size per client times yearly retention ratio (that is, desired monthly retention/12 months), and sum them all giving total image size. 3. Divide the total image size by the native tape capacity, giving the total number of tapes required. Image backup tape calculation To calculate: 1. In our example, we assume that the sum of all of client 3 eligible file spaces for logical volume backup would be 10 GB * 4 = 40 GB. 2. The retention ratio is 1/12. Assuming the previous calculation, this gives 12 * 40 * 0.16 = 76.8 GB. Chapter 2. Implementation planning 55
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