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11. Auto Tiering
This chapter describes an overview and operations of auto tiering.
11.1. Overview
From the perspective of storage features, the performance of SSD is high, but the cost is
also high per GB. Relatively speaking, the cost of traditional hard drive is low, so as
performance is relatively poor. If we follow the 80/20 rule to configure storage systems, all-
SSD configuration is unreasonable for all but the most intensive applications. In fact, SSD
will be needed in only a small part for most typical applications, regardless of whether or not
a critical application, thus giving SSD resources for general storage needs is hugely cost-
prohibitive. Although traditional hard disk performance is enough for general applications
which I/O requirements are not high, the traditional all-hard-drive configuration is also
gradually been inadequate.
On the other hand, the data itself has a lifecycle. Since the data in the course of its life cycle,
it has experienced different levels of activity. In common usage, when creating the data, it is
usually used. As the age of the data increases, it is accessed less often.
The Solution
Therefore, to balance performance and cost factors, adapting a hybrid storage architecture
with a mixture of SSD and traditional HDD seems to be the most reasonable approach for
modern IT environments. Generally, SSD-based storage capacity in 10 to 15% of the total
storage capacity should be enough to fulfill the requirements of critical high I/O applications.
An automated tiering pool is a simple and elegant solution for dynamically matching
storage requirements with changes in the frequency of data access.
Tier Categories
As the name suggestion, auto tiering must have two tiers at least. Automated tiering pool
segregated disk drives into three categories for dual controllers and four for single
controller
 Tier 1: SSD drives for extreme performance tier

Tier 2: SAS drives (15K or 10K SAS HDD) for performance tier
 Tier 3: Nearline SAS drives (7.2K SAS HDD) for capacity tier