Chapter 2. System overview 33
When the image mode volume is created, a direct mapping is made between extents that 
are on the MDisk and the extents that are on the volume. The LBA x on the MDisk is the 
same as the LBA x on the volume, which ensures that the data on the MDisk is preserved 
as it is brought into the clustered system (see Figure 2-14).
Figure 2-14   Image mode volume
Some virtualization functions are not available for image mode volumes, so it is often useful to 
migrate the volume into a new storage pool. After it is migrated, the MDisk becomes a 
managed MDisk.
If you add an MDisk that contains data to a storage pool, any data on the MDisk is lost. 
Ensure that you create image mode volumes from MDisks that contain data before adding 
MDisks to the storage pools.
2.5.17  Easy Tier
IBM Easy Tier is a performance optimization function that automatically migrates or moves 
the extents of a volume across two or more tiers. Easy Tier monitors the host I/O activity and 
latency on the extent of all volumes with the Easy Tier function turned on, in a multitiered 
storage pool, over a 24-hour period.
After this period, the IBM Easy Tier creates an extent migration plan that is based on this 
activity, and then dynamically moves high activity (or hot) extents to a higher disk tier within 
the storage pool. It also moves extent activity that dropped off (or cooled) from the high-tiered 
MDisk back to a lower-tiered MDisk.
The Easy Tier function can be turned on or off at the storage pool and the volume level. The 
automatic storage pool balancing is an integrated part of the IBM Easy Tier engine and is 
enabled by default on all pools. Storage Pool Balancing and IBM Easy Tier do not require 
more licenses within IBM Spectrum Virtualize that is running on IBM Storwize V7000. This 
load balancing feature is not considered an Easy Tier function, although it uses the same 
principles and mechanism.