Mode Category Description Default
MCU/R
CU
By setting the SOMs to ON to lower the upper limit for
each tier, the gray zone between other tiers becomes
narrow and the frequency of page allocation increases.
Note:
1. Apply the mode when the usage of upper tier is low and
that of lower tier is high.
2. The mode must be used with SOM898.
3. Narrowing the gray zone increases the number of
pages to migrate between tiers per relocation.
4. When Tier1 is SSD while SOM901 is set to ON, the
effect of SOM897 and 898 to the gray zone of Tire1 and
Tier2 is disabled and the SOM901 setting is enabled
instead. In addition, the settings of SOM897 and 898 are
effective for Tire2 and Tier3.
Please also see spreadsheet "SOM897_898_901" for more
details about the relations between SOM897, 898 and
901.
899 Volume
Migration
In combination with the SOM900 setting, whether to
execute and when to start the I/O synchronous copy
change as follows.
Mode 899 = ON:
SOM900 is ON: I/O synchronous copy starts without
retrying Volume Migration.
SOM900 is OFF: I/O synchronous copy starts when the
threshold of Volume Migration retry is exceeded.
(Recommended)
Mode 899 = OFF (default):
SOM900 is ON: I/O synchronous copy starts when the
number of retries reaches half of the threshold of Volume
Migration retry.
SOM900 is OFF: Volume Migration is retired and I/O
synchronous copy is not executed.
Note:
1. This mode is applied when improvement of Volume
Migration success rate is desired under the condition that
there are many updates to a migration source volume of
Volume Migration.
2. During I/O synchronous copy, host I/O performance
degrades.
OFF .
900 Volume
Migration
In combination with the SOM8 99 setting, whether to
execute and when to start the I/O synchronous copy
change as follows.
Mode 900= ON:
SOM 899 is ON: I/O synchronous copy starts without
retrying Volume Migration.
SOM900 is OFF: I/O synchronous copy starts when the
threshold of Volume Migration retry is exceeded.
(Recommended)
OFF .
B-22
System option modes
Hitachi Unified Storage VM Block Module Hardware User Guide
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