Backup-to-disk performance tuning


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Implementation headaches
Integrating the storage on existing production servers required more downtime than the company expected. Planning for a minimum of three reboots per server and approximately two hours of downtime for each reboot is adequate, depending on the size of the server. I allowed for additional time on the larger back-end servers, which had more than 12 CPUs and exceeded 2TB of existing storage.

We also paid attention to the performance differences using striped or concatenated volumes. Once the LUNs--sometimes as many as 10--are presented from storage, a volume is created using the host volume manager. Best practices dictate that the best I/O performance is delivered by striped volumes.

Dual pathing on the SAN was also closely examined during the benchmarking phase. Depending on the product, most pathing software works in an active/passive configuration by default. With Symantec's Veritas Dynamic Multipathing (DMP), for instance, specific settings are required to operate in active/active mode. Using the vxdmpadm command, you can observe I/O on each path and determine the current mode of operation. Other pathing software isn't quite this sophisticated. Veritas DMP is also the easiest product to administer and has the widest range of support for disk arrays from various vendors.

During the benchmarking phase, the most labor-intensive task was changing the way the backup storage array was laid out for each round of benchmarks. Each new configuration on the storage array required the existing RAID groups and LUNs to be deleted and then initialized from scratch. This required detailed planning and a lot of patience. Each time the array was reconfigured, it took one day to reconfigure and then one day for the LUNs to finish formatting. Fortunately, the HDS 9570V lets you allocate and use the LUNs at the OS level before they're finished formatting on the array. However, it's not a good practice to perform benchmarks or write production data until the formatting is complete.

This was first published in September 2006

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