Computer Associates BABWBR1151S38 Implementation Guide - Page 29

Storage Capacity Requirements Example: Media Capacities For example, if you try to back up 1 Terabyte on ten media elements that hold 100 GB each (after deducting overhead), media usage will require 100% efficient every time you back up. Because this is unlikely, you need to use eleven media elements. On the other hand, you can back up 1 Terabyte to six cartridges that hold 200 GB each (after deducting overhead), because you have a healthy 200-GB (20%) cushion. The allowances specified above are important. If you do not set aside space for overhead and variations in media usage, you may run out of media during a backup operation and may, consequently, not have a timely and complete backup. Factors Affecting Storage Capacity Calculations Media elements have lifetimes that are usually specified in usage time or numbers of uses or passes across the media. Make sure you take media aging into account when calculating the number of tapes required. Consult the manufacturer's recommendations. Restrictive media-selection criteria and extensive off-site storage can increase your need for media well beyond the minimums calculated previously. Finally, the overall size of the data you need to back up usually increases over time. The amount of data increases faster in some organizations than it does in others, but the total amount almost always increases. The preceding calculations assume a more-or-less constant amount of data. So, when you estimate how much you need to back up (1 terabyte in the examples), always allow for growth. Then check periodically to be sure that you always have enough extra storage to accommodate emerging needs. Testing Plans and Assumptions After you have made the required estimates, performed all the necessary calculations, and formulated a plan that should work for your organization, you should test it. Set up a pilot test configuration using a scaled down environment and run tests. Using the CA ARCserve Backup logs, you can see how good your estimates were. Use the backup logs to: ■ Determine if you estimated the correct amount of backup data correctly by checking the size of a full backup generated by your plan. ■ Check your estimate of the average percent change in your data by checking the size of the incremental backups. ■ Make sure that all the data that should be backed up is backed up. ■ Verify if your data and network segmentation tactics have worked as intended. Chapter 2: Planning Storage Environments 29