HP StoreOnce D2D4324 HP StoreOnce Backup System Concepts and Configuration Gui - Page 15
VTL and NAS Replication overview, Key performance factors with replication
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VTL and NAS Replication overview Deduplication technology is the key enabling technology for efficient replication because only the new data created at the source site needs to replicate to the target site once seeding is complete. This efficiency in understanding precisely which data needs to replicate can result in bandwidth savings in excess of 95% compared to having to transmit the full contents of a cartridge/share from the source site. The bandwidth saving will be dependent on the backup data change rate at the source site. There is some overhead of control data that also needs to pass across the replication link. This is known as manifest data, a final component of any hash codes that are not present on the remote site and may also need to be transferred. Typically the "overhead components" are less than 2% of the total virtual cartridge/file size to replicate. Replication throughput can be "throttled" by using bandwidth limits as a percentage of an existing link, so as not to affect the performance of other applications running on the same WAN link. Key performance factors with replication Key factors for performance considerations with replication: • Define your "seeding" (first replication) strategy before implementation - several methods are available depending on your replication model active/passive, active/active or Many-to-One. See Seeding methods in more detail. • If a lot of similar data exists on remote office StoreOnce libraries, replicating these into a single target VTL library will give a better deduplication ratio on the target StoreOnce Backup system. Consolidation of remote sites into a single device at the target is available with VTL device types. (Catalyst targets can also be used to consolidate replication from various source sites into a single Catalyst store at a DR site.) • Replication starts when the cartridge is unloaded or the NAS share file is closed and when a replication window is enabled. If a backup spans multiple cartridges or NAS files, replication will start on the first cartridge/ file as soon as the job spans to the second, unless a replication blackout window is in force. • Size the WAN link appropriately to allow for replication and normal business traffic taking into account data change rates. A temporary increase in WAN speed may be desirable for initial seeding process if it is to be performed over the WAN • Apply replication bandwidth limits or apply replication blackout windows to prevent bandwidth hogging. The maximum number of concurrent replication jobs supported by source and target StoreOnce appliances can be varied in the StoreOnce Management GUI to also manage throughput and bandwidth utilization. Catalyst Copy and deduplication Catalyst Copy is the equivalent of Virtual library and NAS share replication. The same principles apply in that only the new data created at the source site needs to be copied (replicated) to the target site. The fundamental difference is that the copy jobs are created by the backup application and can, therefore, be tracked and monitored within the backup application catalog as well as from the StoreOnce Management GUI. Should it be necessary to restore from a Catalyst copy, the backup application is able to restore from a duplicate copy without the need to re-import data to the catalog database. The key performance factors are the same as the replication performance factors. Housekeeping Housekeeping is an important process in order to maximize the deduplication efficiency of the appliance. If data is deleted from the StoreOnce system (e.g. a virtual cartridge is overwritten or erased), any unused chunks will be marked for removal, so space can be freed up (space VTL and NAS Replication overview 15