Performing ShadowImage for Mainframe pair tasks, such as creating, splitting, and resynchronizing pairs, can affect host I/O performance on the storage system.
Consider the following items for performance planning.
- Creating pairs
- Take the following actions to minimize the impact of creating pairs on host I/O performance:
- Create pairs when the I/O load is relatively light.
- Limit the number of pairs that you create at the same time.
- Copy pace
- When you are creating, splitting, or resynchronizing pairs, set a slower copy pace. You can enable the local replica option for copy pace. In CCI, set 1 or 2 as the copy pace to select a slower copy pace.
- Number of S-VOLs per P-VOL
- Assigning multiple S-VOLs to a P-VOL uses more storage system resources. Consider limiting the number of S-VOLs per P-VOL.
- VSP One Block 20 series: Load sharing on pools
- Take the following actions to minimize the impact of ShadowImage for Mainframe operations on host I/O performance:
- Separate pools in such a way that the P-VOL and S-VOL belong to different DDP parity groups.
- When performing multiple pair operations simultaneously, place the pairs in such a way that the P-VOL and S-VOL belong to different DDP parity groups.
- If the P-VOL and S-VOL are within the same DDP parity group and you need to perform copy operations on multiple pairs, perform operations for one pair at a time.
- If the storage system becomes overloaded, add drives to the DDP parity group or increase the number of channel boards (CHBs) or disk boards (DKBs).
- VSP One Block 85: Load sharing on parity groups
- Take the following actions to minimize the impact of ShadowImage for Mainframe operations on host I/O performance:
- Evenly divide the primary volume and secondary volume among parity groups.
- When performing multiple pair operations simultaneously, place the pairs in different parity groups.
- If you need to perform copy operations on multiple pairs in the same parity group, perform operations for one pair at a time.
- If the system becomes overloaded, increase the number of parity groups, cache memory, or channel boards (CHBs).
- Storage system configuration
- If you plan to use multiple software applications at the same time, make sure that your storage system is configured for optimal performance, such as sufficient cache memory. Concurrent use affects the performance and operation of the other software applications.
- AIX® host servers
- If you use AIX® host servers, for best performance, place the P-VOLs on one AIX® host server and the paired S-VOLs on another server.
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 SIz 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 might be identified as the P-VOL.
- Quick Restore
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(VSP One B85) To maximize performance when you restore pairs using Quick Restore:
- Use the same RAID level and drive type for the P-VOL and S-VOL.
- Resume the original RAID levels if they were changed by reverse resynchronization.
(VSP One B20 series) You cannot perform Quick Restore for a pair that uses volumes enabled with capacity saving. For DRS-VOLs, use ShadowImage and Thin Image Advanced together. Use ShadowImage to prevent physical failures and pool failures. Use Thin Image Advanced as an alternative high-speed backup method.
CAUTION:(VSP One B85) Do not perform Quick Restore when the P-VOL and S-VOL belong to the different CLPRs. If you do, the CLPRs are switched after the Quick Restore operation finishes.