Performance planning for ShadowImage

ShadowImage User Guide

Part Number

Performing pair tasks, such as creating, splitting, and resynchronizing SI pairs, can affect host server I/O performance on the storage system.

Consider the following items for performance planning:

  • Host server I/O performance and number of SI pairs.
    • Compare the importance of host server I/O performance with the number of SI pairs and the copy pace.
    • Assigning multiple S-VOLs to a P-VOL uses more system resources and lowers the potential performance.
  • Load sharing on parity groups.
    • S-VOLs and P-VOLs should be assigned to different parity groups in case of failure. Make sure that enough parity groups are used to provision the P-VOLs and S-VOLs and provide the performance capability desired.
    • P-VOLs and S-VOLs should be distributed across the appropriate parity groups. If you plan to have multiple copies of the same P-VOLs, consider placing the S-VOLs in different combinations of parity groups.
    • SI can create high levels of internal activity in your storage system. Ensure the configuration is appropriate for the internal and host workload. Items that can help are additional parity groups, cache adapters, cache, BEDs, and MPUs.
    • Limit the number of volumes performing initial copy operations provisioned in the same parity group.
    • If you need to perform copy operations for multiple pairs in the same parity group, perform the operation for a pair at a time.
    • When the system load is high, add a parity group, cache, channel board (CHB), and disk board (DKB). Allocate an S-VOL to the newly installed parity group.
  • If you plan to simultaneously use multiple software applications, make sure that your storage system is configured for optimal performance, such as sufficient cache. Concurrent use affects the performance and operation of the other software applications.
  • If use AIX® host servers, for best performance, place the P-VOLs on one AIX® host server and the paired S-VOLs on another.

    Using a single AIX® host server for the P-VOLs and S-VOLs changes the P-VOL and S-VOLs to the same Port VLAN ID when you create or resynchronize the SI pairs. If the Port VLAN IDs of the P-VOLs and S-VOLs are the same and you reboot the host server, the volumes can be misidentified. For example, the S-VOL can be identified as the P-VOL.

  • Quick Restore. You can maximize performance when you restore pairs using Quick Restore (see Workflow for maximizing Quick Restore performance).

For more information about the guidelines for maximizing host server I/O performance while performing pair operations, see Optimizing host server I/O performance.