HP StorageWorks 6000 HP StorageWorks VLS and D2D Solutions Guide (AG306-96028, - Page 58
Disable Backup Application Verify Pass, Tape Copy or Offload Performance
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servers. In this case, also ensure that bonded/trunk network ports are configured for both the media server and the D2D device. With either configuration there is a requirement to correctly configure the backup application to target the devices correctly; this will usually involve creating multiple backup jobs to back up specific data to selected virtual libraries. Configuring backups to run in parallel rather than serially also improves replication and tape offload operations because these run after backup jobs have completed. Having backups finish at roughly similar times will ensure that the replication and tape offload jobs are not in contention with backup jobs. However, backup application vendors often base their licensing model on the number of tape devices configured, so you may need to balance between performance and cost. Some applications (e.g., HP DataProtector) offer capacity based licensing (per TB) for virtual tape appliances; this licensing model may be more cost effective because it allows you to configure any number of libraries or tape devices. Disable Backup Application Verify Pass Most backup applications will default to performing a verify operation after a backup job. While this offers a very good way to ensure that data is backed up successfully, it will also heavily impact the performance of the whole backup job. Performing a verify operation will more than double the overall backup time due to the fact that restore performance (required for verify) is slower for deduplication enabled devices. Disabling verify for selected backup jobs can be done relatively safely because D2D Backup Systems perform CRC (Cyclic Redundancy Check) checking for every backed up chunk to ensure that no errors are introduced by the D2D Backup System. However, if data is incorrectly written by the backup application but is not corrupt, this will not be detected by the D2D. For this reason, verifying some backup jobs is still recommended. Tape Copy or Offload Performance Copies of cartridges to physical media using the HP D2D Backup System can be achieved by using either a directly attached tape drive or library where the offload is controlled by a manual or scheduled operation from the D2D Web Management Interface, or by using a backup application on the media server to copy data from a cartridge on the HP D2D Backup System to a tape device or library connected to the media server. In either case, take the deduplication process into consideration when scheduling the offload. The D2D allows a tape offload to be automatically scheduled to start immediately after a backup to the virtual tape completes; most backup applications provide a similar configuration option if performing a backup application copy. Take care when using these options because they can result in slower than expected offload performance due to some level of housekeeping running; also, if replication is configured the two operations will clash and result in a delay to replication. You should delay any tape offload for several hours after the backup completes if the backup is doing a significant amount of data overwrite. Otherwise, the housekeeping process will have a detrimental effect on the tape offload performance. As a general rule, for every 100 GB of data on the cartridge being overwritten, allow 30 minutes to pass before starting an offload operation. Because it depends on the deduplication ratio and amount of unique chunks contained in that backup, it is hard to determine how many housekeeping operations will be generated (and therefore how long it will take to run) by an overwrite backup. 58 D2D Systems