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Analysis: Information Lifecycle Management: Page 7 of 29

Mention tiered storage to most IT folks and they think of high-performance Fibre Channel drives for their valuable data and low-cost SATA drives for data that's determined to be of lesser value. That's a start, but storing data in a manner consistent with its business value isn't just about expensive and less-expensive storage on a dollars-per-terabyte basis. Think of storage tiers as providing different SLAs (service-level agreements) rather than just varying costs: The primary storage tier is optimized for performance, with frequent backups to reduce the RPO (recovery point objective), and it's kept small to minimize restore times.

We also must define storage tiers with security in mind--for example, servers accessible only from one side of the Chinese Wall between investment banking and brokerage operations may keep all sensitive data encrypted and have extensive access auditing and controls.

When analyzing savings derived from migrating data between storage tiers, include not just the raw cost-per-gigabyte of disk array acquisition but the fully loaded cost of storing data, including snapshots and DR (disaster recovery) replicas. Take a typical large enterprise: Critical applications are feeding data to a monolithic disk array, say, an EMC Symmetrix or Hitachi TagmaStore. The arrays are configured to take hourly split-mirror snapshots and replicate to one or more DR sites, where snapshots are taken again. These organizations may keep six or more copies of the application's data on its most expensive Tier 1 storage.

If you could identify data that's reached the point in its lifecycle where it's essentially static, and migrate it to a storage environment where only two copies are kept online--one at the primary data center and one at the DR site--you could save a huge amount of disk space. Take advantage of the fact that older, less frequently accessed data can be placed on slower, less expensive storage arrays using RAID 6 and high-capacity SATA drives instead of mirrored Fibre Channel drives, and the savings can be even more significant.

Also bear in mind that as data moves through its lifecycle, the ratio of reads to writes increases substantially, so RAID 5 or RAID 6, with its greater storage capacity and lower write performance compared with mirrored arrays, becomes more attractive.