Chapter 9. Advanced features for storage efficiency 439
9.2 Easy Tier
In today’s storage industry, flash drives are emerging as an attractive alternative to hard disk
drives (HDDs). Because of their low response times, high throughput, and I/O per second
(IOPS) energy-efficiency, flash drives can help a storage infrastructure to achieve significant
savings in operational costs. However, the current acquisition cost per GB for flash is higher
than for Enterprise serial-attached Small Computer System Interface (SCSI) (SAS) and
Nearline (NL) SAS.
Enterprise SAS drives replaced the old SCSI drives. They are common in the storage market.
They are offered in various capacities, spindle speeds and form factors. Nearline SAS is the
low-cost, large-capacity storage drive class, which is commonly offered at 7200 rpm spindle
speed.
It is critical to choose the correct mix of drives and the correct data placement to achieve
optimal performance at the lowest cost. Maximum value can be achieved by placing “hot” data
with high I/O density and low response time requirements on Flash. Enterprise class disks
are targeted for “warm” and Nearline for “cold” data that is accessed sequentially and at lower
rates.
In this section is described the Easy Tier disk performance optimization function of the IBM
Storwize V5000 Gen2. It also describes how to activate the Easy Tier process for both
evaluation purposes and for automatic extent migration.
9.2.1 Easy Tier overview
Easy Tier is an optional licensed function of the IBM Storwize V5000 Gen2 that brings
enterprise storage enhancements to the entry and midrange segment. It enables automated
subvolume data placement throughout different storage tiers to intelligently align the system
with its current workload requirements and to optimize storage usage. This function includes
the ability to automatically and non disruptively relocate data (at the extent level) from one tier
to another tier in either direction to achieve the best available storage performance workload
for an specific environment.
Easy Tier reduces the I/O latency for hot spots, but it does not replace storage cache. Easy
Tier and storage cache solve a similar access latency workload problem, but these methods
weigh differently in the algorithmic construction based on “locality of reference,” recency and
frequency. Because Easy Tier monitors I/O performance from the extent end (after cache), it
is able to pick up the performance issues that cache cannot solve and complement the overall
storage system performance.
In general, the storage environment I/O is monitored on volumes and the entire volume is
always placed inside one appropriate storage tier. Determining the amount of I/O on single
extents is too complex for monitoring I/O statistics, to move them manually to an appropriate
storage tier and to react to workload changes.
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