User guide

System option modes B–9
Hitachi Unified Storage VM Block Module Hardware User Guide
491 ShadowImage Mode 491 is used to improve the performance of
ShadowImage and ShadowImage FCv1.
Mode 491 = ON: The option (Reserve05) of
ShadowImage/ ShadowImage for z/OS is available. If
the option is set to ON, the copy of ShadowImage/
ShadowImage for z/OS/ ShadowImage FCv1 will be
performed from 64 processes to 128 processes so that
the performance will be improved.
Mode 491 = OFF (default): The option (Reserve05) of
ShadowImage/ ShadowImage for z/OS is unavailable.
The copy of ShadowImage/ ShadowImage for z/OS/
ShadowImage FCv1 is performed with 64 processes.
Note:
• Apply mode 491 when the performance of
ShadowImage / ShadowImage FCv1 is important.
• Do not apply the mode when the host I/O
performance is important.
• The mode will be noneffective if 3 or more pairs of
DKAs are not mounted.
• The mode is noneffective for the NSC model.
• Set mode 467 to OFF when using mode 491, since
the performance may not improve.
OFF -
Mode Category Description Default
MCU/
RCU