Mode Category Description Default
MCU/R
CU
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.
901 Dynamic
Tiering
By setting the mode to ON or OFF, the page allocation
method of Tier Level ALL when the drive type of tier1 is
SSD changes as follows.
Mode 901 = ON:
For tier1 (drive type is SSD), pages are allocated until the
capacity reaches the limit. (Without consideration of
performance limitation exceedance, allocation is done
from highly loaded pages until reaching the capacity limit.
When the capacity of the tier1 reaches the threshold
value, the minimum value of the tier range is set to the
starting value of the lower IOPH zone, and the maximum
value of the lower tier range is set to the boundary value.
Mode 901 = OFF (default):
For tier1 (drive type is SSD), page allocation is performed
based on performance potential limitation. (With
consideration of performance limitation exceedance,
allocation is done from highly loaded pages but at the
point when the performance limitation is reached, pages
are not allocated any more even there is free space)
When the capacity of the tier1 reaches the threshold
value, the minimum value of the tier range is set to the
boundary value, and the maximum value of the lower tier
range is set to a value of boundary value x 110% + 5
[IOPH].
Note:
1. This mode is applied when pages with the maximum
capacity need to be allocated to tier1 (drive type is SSD)
with DT or DTz.
2. 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.
3. The following is recommended when applying SOM901.
The actual I/O value (total number of I/Os of all tiering
policies) < the performance potential value of Tier 1*1 x
0.6 *1: The performance potential value of Tier 1
displayed on Monitor information by using Dx-ray. Please
OFF
System option modes
B-23
Hitachi Unified Storage VM Block Module Hardware User Guide
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