HP StorageWorks 6000 HP StorageWorks VLS and D2D Solutions Guide (AG306-96028, - Page 59
Tape Library Emulation, Emulation Types, Cartridge Sizing, Number of Libraries per Appliance
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In addition, consider other operations running on the D2D. For example, if multiple backups finish at different times, each may result in some housekeeping work. Add all of the data backup amounts together to get an idea of the time that housekeeping will take. Tape Library Emulation Emulation Types The HP D2D Backup Systems can emulate several types of HP tape library devices, and the maximum number of drives and cartridge slots is defined by the type of library configured. However, performance is not related to library emulation except in the ability to configure multiple drives per library and thus enable multiple simultaneous backup streams. Cartridge Sizing The size of a virtual cartridge has no impact on its performance. HP recommends that cartridges are created to match the amount of data being backed up. For example, if a full backup is 500 GB, you should select 800 GB, the next larger configurable cartridge. If backups span multiple cartridges, you risk a performance impact because housekeeping operations will start on the first backup cartridge as soon as the backup application spans to the next cartridge. Number of Libraries per Appliance The D2D appliance supports creating multiple virtual library devices. If large amounts of data are backing up from multiple hosts or for multiple disk LUNs on a single host, you should separate these across several libraries (and consequently into multiple backup jobs). Each library has a separate deduplication "store" associated with it, and reducing the amount of data and complexity of each store will improve its performance. Creating a number of smaller deduplication stores rather than one large store which receives data from multiple backup hosts can have an impact on the overall effectiveness of deduplication. However, generally the cross server deduplication effect is quite low unless you are storing a lot of common data. If you store a large amount of common data on two servers, HP recommends that you back these up to the same virtual library. Optimizing Rotation Scheme to Reduce Housekeeping Reducing the frequency of full backup cartridge reduces the amount of deduplication housekeeping overhead required. You can optimize it using the following: • Longer retention policy: Deduplication has little penalty for using a large number of virtual cartridges in a rotation scheme and therefore a long retention policy for cartridges (most data will be the same between backups and therefore deduplicated), which reduces the number of overwrites. • Full vs. incremental/differential backups: The requirement for full or incremental backups is based on how often offsite copied of virtual cartridges are required and on speed of data recovery. If regular physical media copies are required, the best approach is that these are full backups on a single cartridge. Speed of data recovery is less of a concern with a virtual library than with physical media. For example, if a server fails and needs to be fully recovered from backup, the recovery will require the last full backup plus every incremental backup since (or the last differential backup). Finding and loading multiple physical cartridges is time-consuming. However, with virtual tape there is no need to find all of the pieces of media. Because the data is stored on disk, the time to restore is lower due the ability to randomly seek more quickly within a backup and load a second cartridge instantly. HP StorageWorks VLS and D2D Solutions Guide 59