IBM E16RMLL-I Implementation Guide - Page 76
Disk storage pool size, Archive disk sizing
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migration to the next storage pool can execute concurrently; however, performance will degrade. We recommend using a primary disk storage pool of at least the recommended size to reduce interference from migration while backup is running. 2.8.9 Disk storage pool size To estimate a primary storage pool size if running backup cycles only, do the following: 1. Using Table 2-1 on page 18, multiply the GB changed per backup by (1 - the Data compression rate) to give the total bytes transferred for each client. 2. Sum the total bytes transferred for all clients to give the total bytes transferred per backup cycle. 3. Add 15% to total bytes transferred per backup cycle to give the storage pool size. This allows for variability in the size and number of files per backup. For example, using the sample figures in Table 2-1 on page 18, the GB changed per backup are 6 * 20 (120 GB) and 4 * x 100 (400 GB), while the data compression figures are 0.5 and 0.66, respectively. 1. Multiplying 120 by (1 - 0.5) gives 60, and multiplying 400 by (1 - 0.66) gives 136. 2. Summing 60 and 136 gives 196 GB. 3. Adding 15% gives a storage pool size of 225.4 GB. We will round to 226 GB. 2.8.10 Archive disk sizing In most environments, archive disk sizing is less critical than for backup. This is because backup operations tend to run much more frequently (usually nightly) and to a stricter time frame. Archives may run less frequently, and on weekends when the overall workload is lighter. Since in these circumstances the impact of running concurrent archive and storage pool migration might not be so critical, it is not normally necessary to use the full archive size in calculating storage pool requirements. Another factor to be considered for sites that are doing frequent archiving of large amounts of data, where the storage pool and processing impact are great, is the possibility of substituting backup set operations for archive. The advantage of this is that generating a backup set requires the Tivoli Storage Manager server only-the client is not involved in any way since the backup set is created using data that has already been sent to the server in normal backup operations. 46 IBM Tivoli Storage Manager Implementation Guide