Evaluating opportunities: Moving data between storage tiers

Storage Networking World - A new tier in the storage hierarchy has firmly taken root. It's called secondary storage and is defined as disk storage that is less expensive and lower performing than primary disk storage. Many vendors now have secondary storage offerings, with others planning to catch up shortly.
The interesting thing to look at is how data is being moved between these storage tiers. It is best to start with how secondary storage is commonly used.
One of the early promotions of secondary storage was as a disk-to-disk backup solution. The business value was based on the "time to recovery" of data. The economics of recovering data to resume operations may vary by company, but the concept is well understood. The economic advantages gained in the timeliness of recovering data from disk rather than tape may easily justify the cost.
But where disk-to-disk backup is not always understood is in the operational characteristics of data recovery to meet RTO, or recovery time objectives. A simplistic approach is to use the same backup utilities as for tape, thereby putting data on disk in tape backup format, which means tape recovery procedures are needed to get data from disk.
The better solution is to make copies of data on the secondary storage from primary storage in the normal disk format, and allow recovery through appropriate means, including mounting file systems for individual file recovery or through application recovery routines. An operational change is required to make the disk copies through utilities, special software or mirroring hardware, but the gains in recovery time and overall usability seem worth the investment.

From recovery to access
Another use for secondary storage is for data that has changed from highly active to less active. This is an exploitation of the "time value of data," whereby a majority of the data becomes less frequently accessed as it ages. Moving the data to less costly and perhaps lower performing storage is an economic decision that may make sense in many environments. Many of the implementations for this type of secondary storage have been based on manual or scripted procedures to this point.
Using secondary storage for data that is changed infrequently, if ever, and is accessed with an unknown pattern is what has been termed "fixed content" or "reference data." The value has been that this data typically did not previously exist under the domain of IT but was on other types of media (print, tape, optical, etc.) and under control of other organizations. While it represents a new demand