IBM DS8880 Series Introduction And Planning Manual page 74

The Easy Tier Heat Map Transfer utility replicates Easy Tier primary storage
workload learning results to secondary storage sites, synchronizing performance
characteristics across all storage systems. In the event of data recovery, storage
system performance is not sacrificed.
You can also use Easy Tier to help with the management of your ESE thin
provisioning on fixed block (FB) or count key data (CKD) volumes.
An additional feature provides the capability for you to use Easy Tier manual
processing for thin provisioning. Rank depopulation is supported on ranks with
ESE volumes allocated (extent space-efficient) or auxiliary volumes.
Use the capabilities of Easy Tier to support:
Drive classes
Three tiers
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DS8880 Introduction and Planning Guide
The following drive classes are available, in order from highest to lowest
performance. A pool can contain up to three drive classes.
Flash Tier 0 drives
The highest performance drives, which provide high I/O
throughput and low latency.
Flash Tier 1 drives
The first tier of high capacity drives.
Flash Tier 2 drives
The second tier of high capacity drives.
Enterprise drives
SAS (10-K or 15-K RPM) disk drives.
Nearline drives
Nearline (7.2-K RPM) disk drives, which provide large data
capacity but lower performance.
Using three tiers (each representing a separate drive class) and efficient
algorithms improves system performance and cost effectiveness.
You can select from four drive classes to create up to three tiers. The drives
within a tier must be homogeneous.
The following table lists the possible tier assignments for the drive classes.
The tiers are listed according to the following values:
0 Hot data tier, which contain the most active data. This tier can also
serve as the home tier for new data allocations.
1 Mid-data tier, which can be combined with one or both of the
other tiers and will contain data not moved to either of these tiers.
This is by default the home tier for new data allocations.
2 Cold data tier, which contains the least active data.