Contributing Author: David Floyer
The basic purpose of this article is to allow business and IT staff to understand tiered storage, its potential organizational impact, possible drawbacks and the maturity of both the underlying technology and the supporting software and services ecosystem.
What is tiered storage?
- Tiered storage is a system of assigning applications to different types of storage media based on application requirements. Factors considered in the allocation of storage type include the level of protection needed, performance requirements, speed of recovery, and many other considerations. Since assigning application data to specific media may be complex, some vendors provide software for automatically managing the process.
Figure 1 below helps explain where different types of storage are used in a typical data center, and the strategic fit of a corresponding storage approach. On the vertical axis is the importance of data availability and performance. Storage in tiers 1 & 2 support the most important applications to the organization, and tiers 2 & 4 support less mission critical applications. On the horizontal axis is the type of application that uses the data (operational or reference). In general there is a trend towards more data being mission critical, and a higher growth rate of reference data particularly driven by increased governance and regulatory requirements that mandate keeping data for longer periods of time.
The mission critical operational applications are in the top left hand corner. These are often database transactional systems, with a lot of reusable data suitable for caching, with high performance and recoverability requirements. Larger servers are driving the applications in this segment. The bottom right hand corner is often characterized by a large number of smaller servers and greater emphasis on connectivity.
As the amount of information grows, the challenge for the storage management staff is how to manage and optimize the different types of storage.
The importance of Figure 1 from a storage management perspective is a single storage solution is almost never appropriate for the entire data center. Having all storage with high functionality for example is not necessary or cost effective. Typically, one size does not fit all in the data center.
How does tiered storage work?
Conceptually, tiered storage is often depicted as a pyramid. In practice tiered storage involves software, hardware, processes and tools that facilitate the management of different classes of storage services across a wide range of workloads and applications. Key tiered software components include classification tools, monitoring and chargeback mechanisms, high performance data movers, hierarchical storage managers, access control facilities and resource managers which invoke or interact with a variety of storage services such as copy, backup and encryption.
Typically, storage tiers have grown as a function of individual application requirements and storage managers have been forced to develop enterprise architectures on the existing infrastructure in place. This has led to the need for a variety of storage management software techniques that rely on classifying data, data placement, data movement, backup and recovery and other management processes implemented across the device spectrum.
Why tiered storage?
There are three main strategic choices in managing a diverse and complex set of storage, which are:-
- Mix, Match and Manage
This is the most common approach taken in data centers. The best fit of storage is applied to each appropriate application and the storage staff manages a diverse set of resources.
- One storage system for all storage
Assuming high-end storage is used, this approach provides the lowest cost of administration and highest service levels to the user. The disadvantage is capital budget “sticker shock.” Alternatively, using low-end storage for all creates the reverse scenario – lower capital outlays, much higher overall costs of managing the storage.
- A tiered storage software storage management overlay
Storage management software (either Server based or storage controller based) can provide an overall umbrella of functionality to all storage. For example, storage virtualization functionality can be provided by this type of software independent of the storage devices. The advantage of this approach is minimized storage costs, and common storage management processes and procedures across all types of storage. The disadvantages of this approach is the cost of the software, the potential tie-in to a vendors software, and the costs and risks of implementation.
Tiered Storage has the potential to significantly reduce the costs of storage and storage management functionality in environments when the cost of implementation and servicing is justified.
When tiered storage is justified
As stated above, a large number of data centers currently achieve a type of tiered storage environment by providing pools of different types of storage. The disadvantage of this approach is that different storage management software is usually required for each pool. Once an application has been assigned to a pool, it is difficult and expensive to migrate the application to another storage pool. There are also inherent costs in managing multiple different storage pools.
Tiered storage implementations are easiest to justify when:
- There is significant change in the applications being delivered to the business
- When there is a diverse set of applications providing services to many different parts of the organization
- When the number of storage staff and the amount of storage are significant (unlikely to be achieved in small business data centers)
- When there is good communication between the organization and IT on being able to define the business benefits of matching storage to the application
- When IT has a good track record of deliving business value through its IT infrastructure.
Software and services to implement Tiered Storage are still maturing, and there are a wide range of potential solutions in the market place. Tiered storage consultants are in general wed to specific solutions that they know and have implemented. Practices that analyse the strategic choices of tiered storage solutions have yet to emerge.
In practice, this means that the majority of tiered storage software and services are being provided by storage vendors such as EMC, Hitachi, HP, IBM, NetApp, Sun and many other smaller vendors.