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Different tiers
Tiering storage is one of the biggest drivers of data migration. According to a recent survey of Storage magazine readers regarding their migration strategies for tiered storage, nearly half tier storage: of these, almost 21% have four or more tiers, approximately 46% have three tiers and 33% have two tiers of storage. Thirty-four percent of those surveyed say that 31% to 50% of their data resides on Tier 1 storage. Not surprisingly, 40% rely on manual methods for moving data between tiers, approximately 20% use automated methods and the remainder use a combination of both (see "

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Snapshot: Cheers and jeers for tiered storage").

Rudolph Technologies' Fitch regularly performs data migrations between multiple tiers of storage (see "Old data isn't the only candidate for tiering," below). "We have two different tiers of storage: Fibre Channel and Serial ATA drives," says Fitch. "The Compellent Data Progression Module that's part of Storage Center lets us automatically move data between Tier 1 and Tier 3 storage nondisruptively."

Fitch just sets a threshold for the number of days of nonuse for data. "Image files that aren't refreshed frequently are moved down to Tier 3 storage automatically. Only frequently accessed files stay up on our large, expensive Fibre Channel drives," he notes.

Data migrations are a fact of life and automating the tedious process can be well worth the effort. Users have found that host-based software is perhaps the best for application-specific migrations such as database replication. It frees the storage array of processing and can often be used more easily for migrating data between heterogeneous storage.

Array-based migration, such as that used by Compellent Technologies' customers, has also proven to be popular, and legions of customers use EMC's Symmetrix Remote Data Facility to move data between EMC arrays. Many users also rely on their chosen array's data utilities to migrate data from one array to another or to move data between tiers. Array-based migration from one array to another is a popular option not only for technology refreshes, but for heterogeneous storage migration. Finally, the use of a network appliance provides additional flexibility for moving file-, block- or volume-based data among heterogeneous devices.

Old data isn't the only candidate for tiering
Moving data among tiers of storage isn't as easy as it may seem. Many users move data based on its age or length of inactivity. However, there are other criteria for the movement of data that you should consider:

Medical and Patient Information: Moving this type of data depends on the age of the patient. If the data is about a child, it must be accessible for as long as 21 years. If the patient is an adult, data needs to be available, according to differing state laws, for the life of the patient; some states also require availability for a period of time after the adult patient dies. Maintaining this type of information, which may be needed immediately in the event of a medical crisis, is best done on Tier 1 storage for current and recent patients, and on Tier 2 storage for patients seen less recently.

Intellectual Property: Here again, the age of the data isn't a factor for where it should be stored. Many users store intellectual property data that's core to their businesses on Tier 1, which is readily accessible storage.

Electronically Stored Information (ESI): This data, comprising personnel records or any other company information that could be the subject of litigation against the company, is often stored on Tier 1, 2 or 3 devices. If the data becomes relevant to a lawsuit, it must be readily accessible and searchable. The data must be tiered in an appropriate manner so it can be accessed quickly; in some cases, this requires moving some Tier 3 data stored on tape back to Tier 2 or Tier 1 disk storage. Many email applications support the tiering and migration of emails.

This was first published in June 2008

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