New page assignment: New pages are assigned based on a number of optional settings. Pages
are then assigned to the next lower tier, leaving a buffer area (2% per tier by default) for tier
relocation. Once 98% of capacity of all tiers is assigned, the remaining 2% of the buffer space is
assigned from the upper tier. The buffer space for tier relocation is 2% in all tiers. The following
illustrates the workflow of new page assignment.
Figure 11 Workflow of a new page assignment
Setting external volumes for each tier
If you use external volumes as pool-VOLs, you can put the external volumes in tiers by setting the
External LDEV Tier Rank for the external volumes. The External LDEV Tier Rank consists of the
following three types: High, Middle, and Low. The following examples describe how tiers may be
configured:
Example 1: When configuring tiers by using external volumes only
Tier 1: External volumes (High)
Tier 2: External volumes (Middle)
Tier 3: External volumes (Low)
Example 2: When configuring tiers by combining internal volumes and external volumes
Tier 1: Internal volumes (SSD)
Tier 2: External volumes (High)
Tier 3: External volumes (Low)
You can set the External LDEV Tier Rank when creating the pool, changing the pool capacity, or
setting the Edit External LDEV Tier Rank window. The following table explains the performance
priority (from the top) of data drives.
Data drive typePriority
SSD1
SAS 15K rpm2
SAS 10K rpm3
SAS 7.2K rpm4
External volume* (High)5
External volume* (Middle)6
Smart Tiers 87
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