Hitachi Virtual Storage Platform G400, Reference Manual

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(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 Mode 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:
(for HUS VM)
(Write Pending capacity of the entire system of concerned
MPB) ÷ (Cache capacity of the entire system of concerned
MPB)
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, it is limited to set Mode 454 to ON
only when a CLPR has constant high workload and it gives
priority to I/O performance in a CLPR with low workload
than host I/O halt in the CLPR with high workload.
Notes:
(1) When this System Option Mode 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 System Option Mode to ON only
when the overloaded state of a specific CLPR would not
affect other CLPRs.
In the case where the HUR 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 either.
Therefore it is recommended to set this System Option
Mode 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) may occur.
457
(1) High Speed LDEV Format for External Volumes
The high speed LDEV format for external volumes is
available by setting System Option Mode 457 to ON. If
System Option Mode 457 is ON, when selecting the external
volume group and performing the LDEV format, any Write
processing on the external LUs will be skipped. However, if
OFF
54 System option modes
Hitachi Virtual Storage Platform G400, G600 Hardware Reference Guide