With storage needs spiraling upward, it's simply impractical to keep every piece of corporate data on expensive, high-performance Fibre Channel discs.
The practice of tiered storage has emerged as a way to mitigate this expense by keeping mission-critical data on the fastest disc platforms while relegating less valuable data to slower and less expensive storage, such as SATA disc or even tape. In most cases, an organisation will establish and maintain several different storage tiers. But, organising corporate data into tiers is hardly straightforward.
First, data must be classified to understand the relative value of each file or file type. Data types that are only infrequently accessed, such as email, are often indexed and stored with automated archiving tools. Data then has to be migrated between storage platforms so that it can be stored according to its classification. This Buying Guide covers the major product considerations involved in tiered storage initiatives. Each chapter offers a set of buying points and product specifications that can help readers identify prospective new tiered storage products. Before we look at specific product categories, let's start by identifying the core concerns when considering tiered storage.
Establish data retention policies in advance. Most organisations are obligated to retain certain data types in order to meet compliance and litigation needs and then delete that data after its retention period expires. However, retention policies are not set automatically -- no software can tell you how long you should keep a piece of data. Instead, retention is defined by understanding the value of each data type and its relationship to compliance. Data migration and archiving tools can then be used to enforce the established retention policies across your storage tiers.
Have a data categorisation plan formulated in advance. Data classification is not automatic -- no software can determine the actual value of data to your own organisation, so don't rely on data classification tools to make classification decisions for you. Data classification is a human process that involves understanding and input from many departments, like human resources, finance and legal. Once you have established the relative value of each data type, data classification tools can then find the data, apply metadata and enforce established retention policies. Experts note that the most successful tiered storage deployments occur when categorisation and retention policies are already mature and proven.
Consider the management impact of additional storage systems. Tiered storage often involves the use of multiple storage systems, and this can sometimes present more of a burden for storage administrators. For example, Tier 1 storage may reside on a Fibre Channel storage area network (San), Tier 2 storage may reside on a SATA network attached storage (Nas) and Tier 3 storage may exist on a content-addressed storage (CAS) archiving system, virtual tape library (VTL) or tape library. For some organisations, the added cost and management overhead imposed by multiple storage tiers can overcome the benefits, and experts note that some large data centers are actually abandoning their tiered storage in favor of a single tier.Set realistic savings expectations. While the ultimate objective of tiered storage is to save money, the actual savings often falls below expectations. For example, experts note that Tier 2 storage should cost 20% to 30% less than Tier 1, while Tier 3 storage should cost 50% to 60% less. In actual practice, however, experts only see a savings of 10% to15% at Tier 2 and only 30% to 40% savings at Tier 3. Below expectation savings is another reason why some enterprises revert to a single storage tier. Buy the tool that best fits your needs. You will find a multitude of migration, archiving and data classification tools to help automate your own tiered storage environment. But, there can be a tremendous difference in the complexity, cost and capability of those tools. There are many possible examples. Some products may offer a relatively simple and focused tool, like Brocade Communications Systems Inc.'s Data Migration manager, while other products may provide a sophisticated suite of functions, like Enterprise Vault. Similarly, you may select a tool that is intended for a specific storage platform, such as EMC Corp.'s SRDF or opt for a more heterogeneous tool, such as Incipient Inc.'s Network Storage Platform (NSP). Finally, some tools may address specific applications, such as Mimosa Systems Inc.'s NearPoint for Microsoft Exchange Server, while other tools may support a wide range of applications. Experts suggest that you focus on meeting your minimum performance criteria, rather than being distracted by potentially unnecessary value-added features. Consider the potential for performance improvements. When all storage is located on a single tier, the contention for user and application access can adversely influence storage system performance. That contention can ease by spreading out access across multiple storage tiers. Even though SAS or SATA drives may offer lower performance than Fibre Channel drives, reduced competition for access may actually allow for good performance at the SAS or SATA tier. And, since this also reduces the number of requests arriving at Fibre Channel drives, the top tier performance may also improve. Return to the beginning
This was first published in July 2007