Hitachi VSP G200 System Administration Manual page 356

Mode Category
457 Universal Volume
Manager
356
System Administrator Guide for VSP Gx00 models and VSP Fx00 models
Description
Mode 454 = OFF (default): The amount of the entire
destage processing is periodically determined by using the
highest workload of all CLPRs (*a). (The larger the workload
is, the larger the amount of the entire destage processing
becomes.)
*a: (Write Pending capacity of CLPR#x of concerned MPB) ÷
(Cache capacity of CLPR#x of concerned MPB), x=0 to 31
CLPR whose value above is the highest of all CLPRs
Because the destage processing would be accelerated
depending on CLPR with high workload, when the workload in
a specific CLPR increases, the risk of host I/O halt would be
reduced.
Therefore, set SOM 454 to OFF in most cases.
Mode 454 = ON:
The amount of the entire destage processing is periodically
determined by using the workload of the entire system (*b).
(The larger the workload is, the larger the amount of the
entire destage processing becomes.)
*b: (Write Pending capacity of the entire system of
concerned MPB) ÷ (Cache capacity of the entire system of
concerned MPB)
Caution: Because the destage processing would not be
accelerated even if CLPR has high workload, when the
workload in a specific CLPR increases, the risk of host I/O
halt would be increased. Therefore, set SOM 454 to ON only
when a CLPR has constant high workload and the I/O
performance in a CLPR with low workload has higher priority
than host I/O halt in the CLPR with high workload.
Notes:
1. When this SOM is set to ON, even if there is an
overloaded CLPR (CLPR with large Write Pending
capacity), the amount of destage processing would not
increase easily. Therefore TOV(MIH) may occur in the
overloaded CLPR. Set this SOM to ON only when the
overloaded state of a specific CLPR would not affect
other CLPRs.
When the UR function is used, if user volumes and
journal volumes are defined in different CLPRs, when
the CLPR to which the journal volumes are assigned
overflows, the user volumes become inaccessible.
Therefore it is recommended to set this SOM to OFF.
2. Because the destage processing will have a lower
priority in the overloaded CLPR, the overloaded state of
the overloaded CLPR is not removed, and TOV(MIH)
might occur.
This SOM has two purposes: High-Speed LDEV Format for
External Volumes, and Support for Mainframe Control Block
Write GUI.
Mode 457 = ON:
System option modes
Default MCU/RCU
OFF Both