HP StorageWorks 6000 HP StorageWorks VLS and D2D Solutions Guide (AG306-96028, - Page 43
Copy to Tape using D2D Tape Offload, Copy to Remote Disk Backup Device using Replication
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virtual tapes will not be created. Subsequent backups will fail because the virtual tapes present are protected. NOTE: Automigration echo copy is not suitable for use with deduplication because: • You cannot use echo copy to create archive tapes from the replication target device because these must have a different barcode, retention time, cartridge size, and contents. They must be created by another instance of the backup application. (See Creating Archive Tapes from the Replication Target.) • Echo copy acts as a disk-cache to the physical tapes, so when physical tapes are ejected from the library (for example, to be sent off-site) this also ejects the matching virtual cartridges into the Firesafe; they are disabled in the deduplication system. • Echo copy only copies whole cartridges and because the size of deduplicated virtual cartridges is generally 50-200 GB, a large amount of tape capacity would be wasted if LTO3 or LTO4 physical tapes were used. Copy to Tape using D2D Tape Offload You can offload cartridges to physical tape using a tape drive or library that is physically attached to the D2D system via SAS or pSCSI and is not visible to the backup application. This solution offers the following benefits: • Tape offload can be conducted during normal working hours without affecting network performance because no data is sent over the network during the offload. • Cartridges can be offloaded at the maximum read performance for a virtual library which makes this process relatively fast. • Offloaded cartridges are in backup application format, so you can use it to directly restore data using a tape drive attached to a media server if necessary. However, you must take into account a number of shortfalls of this configuration: • The backup application cannot track the physical cartridges because it played no part in their creation. A cartridge copied by the D2D is only valid for as long as the virtual cartridge remains current; if the virtual cartridge is modified (overwritten or appended), the physical cartridge content no longer has a valid entry in the backup application database. However, you could still use it for disaster recovery if you lost the backup application database. Creating long rotation schemes where cartridges are overwritten infrequently works well with this model. • Even with the scheduling features provided in the D2D GUI, offloads are hard to accurately schedule to coincide with completion of the original backup. Do not use physical tape offload as a way to free up space on the D2D by removing the virtual cartridge after an offload. Doing this will not save space due to the deduplication effect and will result in backup application database entries becoming invalid. In addition, HP does not recommend using physical media to extend the retention period of a backup (i.e., keeping a physical cartridge beyond the point where its associated virtual cartridge has been overwritten) because the backup application database will become inconsistent with the backup on tape. Copy to Remote Disk Backup Device using 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 HP StorageWorks VLS and D2D Solutions Guide 43
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