HP StorageWorks 6000 HP StorageWorks VLS and D2D Solutions Guide (AG306-96028, - Page 23

Tape Oversubscription Deduplication requires more virtual tape capacity than physical disk; this is sometimes called tape oversubscription. The purpose of deduplication is to reduce the amount of disk required to store multiple generations of backups. Be sure to create enough virtual tape capacity to contain your entire retention policy, and the amount of physical disk will be much less capacity due to deduplication. For example, if you are backing up 50 TB per week and retaining four weeks, you need to create enough virtual tape capacity (after compression) to store 200 TB of backups. If you have 2:1 compression, you must create 100 TB of virtual tape capacity to hold the four weeks of backup data. Given deduplication across the four weeks of backup versions, the amount of physical disk required for this 100 TB of virtual tape would be significantly less. NOTE: Do not create too much virtual tape capacity or your backup application may be set to prefer to use blank tapes instead of recycling older tapes. You would likely run out of disk space because the older backups are not being recycled/overwritten and thus the disk space used by these old backups is not freed up. As in the example above, you should create enough virtual tape capacity to hold backups for your entire retention policy but no more. Replication Introduction to Replication Deduplication can automate the off-site process and enable disaster recovery by providing site to site deduplication-enabled replication at a lower cost. Because deduplication knows what data has changed at a block or byte level, replication becomes more intelligent and transfers only the changed data instead of the complete data set. This saves time and replication bandwidth, and is one of the most attractive features that deduplication offers. Replication enables better disaster tolerance with higher reliability but without the operational costs associated with transporting data off-site on physical tape. You can take control of your data at its furthest outposts and bring it to the data center in a cost-effective way. Using replication, you can protect data anywhere. HP StorageWorks VLS and D2D Solutions Guide 23