Hitachi VSP G200 System Administration Manual page 371

Mode Category
897 Dynamic Tiering
898 Dynamic Tiering
System Administrator Guide for VSP Gx00 models and VSP Fx00 models
Description
occurs and the write performance degrades because of
an increase in write pending rate.
2. When the background format function is enabled,
because up to 42 MB/s of ECCG performance is used,
local copy performance may degrade by about 10%.
Therefore, confirm whether the 10% performance
degradation is acceptable or not before enabling the
function.
3. When a Dynamic Provisioning VOL on an external
storage system, which is used as an external VOL, is
used as a pool VOL, if the external pool on the external
storage side becomes full due to the background
format, the external VOL may be blocked.
If the external pool capacity is smaller than the external
VOL capacity (Dynamic Provisioning VOL of external
storage system), do not enable the background format
function.
4. If the background format function is disabled by
changing this SOM setting, the format progress is
initialized and the entire area becomes unformatted.
5. The background format for FMC drives is not disabled.
When FMC drives are used, use SOM 1093.
By the combination of SOM 897 and 898 setting, the
expansion width of Tier Range upper I/O value (IOPH) can be
changed as follows.
Mode 897 = ON:
• SOM 898 is OFF: 110%+0IO
• SOM 898 is ON: 110%+2IO
Mode 897 = OFF (default):
• SOM 898 is OFF: 110%+5IO (default)
• SOM 898 is ON: 110%+1IO
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.
Notes:
1. Apply this SOM when the upper tier usage is low and
lower tier usage is high.
2. This SOM must be used with SOM 898.
3. Narrowing the gray zone increases the number of pages
to migrate between tiers per relocation.
4. When Tier1 is SSD while SOM 901 is set to ON, the
effect of SOM 897 and 898 to the gray zone of Tier1
and Tier2 is disabled and the SOM 901 setting is
enabled instead. In addition, the settings of SOM 897
and 898 are effective for Tier2 and Tier3.
For more details about the interactions between SOMs 897,
898, and 901, contact customer support (see
SOM897_898_901 sheet).
By the combination of SOM 898 and 897 setting, the
expansion width of Tier Range upper I/O value (IOPH) can be
changed as follows.
System option modes
Default MCU/RCU
OFF -
OFF -
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