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Storage tiers
Maximizing storage utilization and growing storage on an as-needed basis results in significant storage savings. Storage costs can be further reduced by providing different tiers of storage to applications and users by segregating the storage pool into different classes based on performance, service level and cost. Offering three different storage tiers is the most popular approach (see "Tiers offer service and savings," below).

Tiers offer service and savings
An important aspect of running storage as a utility is the ability to provide different tiers of storage with varying service levels and cost. The number of tiers, their characteristics and the size of each tier depends on the specific environment. For instance, 65% of National Medical Health Card (NMHC) Systems Inc.'s storage is Tier 1 because a large percentage of it is used for database apps. Conversely, environments with a large number of file stores are likely to have a higher percentage of Tier 2 or Tier 3 storage.

In addition, the definition of storage tiers is very relative. What's considered Tier 1 storage in one company may serve as Tier 3 in other places. "Tiering is

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very customer specific; some customers consider [EMC] Clariion as Tier 1, while others view only [EMC] Symmetrix as Tier 1," explains Kevin Gray, product marketing manager for storage products at EMC Corp.'s resource management group.

Although storage tiers can't necessarily be pinned down in absolute terms, storage tiers--especially Tier 1 storage--do have common characteristics. Tier 1 storage is typically characterized by high performance, high availability, scalability, expandability and higher cost. Tier 1 storage is likely to offer more advanced features than lower tier storage, like the types of supported interfaces, cloning, snapshots, and synchronous and asynchronous replication. Array vendors have structured their offerings to support a three-tier approach to storage and, in general, high-end arrays like EMC Symmetrix, Hitachi Data Systems' TagmaStore Universal Storage Platform or Hewlett-Packard Co.'s StorageWorks XP arrays are likely to serve the critical Tier 1 storage layer.

Besides the choice of the storage array, Tier 1 storage must provide the most aggressive service levels related to backup, restore and disaster recovery (DR). Although the objectives for recovery and DR are company specific, Tier 1 storage is likely to serve mission-critical apps that may have zero tolerance for downtime. As a result, Tier 1 storage frequently uses snapshots, replication or continuous data protection that provides real-time backup, close to instantaneous restores and the ability to restore to any point in time. For the most critical of applications, synchronous replication to a secondary array or nodes in a clustered architecture can provide instantaneous failover with zero downtime.


This was first published in December 2007

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