OpenVMS documentation

Several factors affect the performance of a shadow set, including the following:

I/O access path (local versus remote)
Size of I/O requests
Data access patterns (random or sequential)
Read-to-write ratio
Shadow set configuration
State of a shadow set (steady or transient)
Whether you use the shadowing copy and merge performance assists (see “Improving Performance for Merge and Copy Operations ”)
Whether you use the minicopy operation (see Chapter 7 “Using Minicopy for Backing Up Data (Integrity servers and Alpha)”)
Whether you use HBMM (see Chapter 8 “Host-Based Minimerge (HBMM) ”)
Other work load on the system utilizing common resources (CPUs, disks, controllers, interconnects)
Striping (RAID) implementation

The following sections examine how the state of a shadow set and its configuration can affect resource utilization and performance. Some guidelines for controlling the use of system resources are also provided in “Guidelines for Managing Shadow Set Performance”. Because there is no significant difference in the performance of a nonshadowed disk and a one-member shadow set, all discussions that follow apply to multiple-member shadow sets.

HP OpenVMS Systems Documentation

Factors That Affect Performance of a Shadow Set