Tier 0 (tier zero) is a level of storage that’s faster, and perhaps more expensive, than any other level in the storage hierarchy.
While CPU speeds and hard disk drive capacities have been increasing exponentially, hard disk drive input/output per second (IOPS) have only improved slightly, putting constraints on application performance. One way IT administrators have compensated is to tier application data storage and use faster, more expensive hard disk drives for some things and slower, less expensive hard disk drives for others. This is known as hierarchical storage management (HSM). The goal of HSM is to increase service levels to critical applications and data sets, while reducing the overall cost of data storage.
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In general, the lower the tier’s number in a tiered storage hierarchy, the more expensive the storage media and the less time it takes to retrieve data. An enterprise that requires selected applications to be accessed very quickly may choose to use expensive single-level cell (SLC) solid state storage in its very highest tier, which some storage professionals are calling tier 0.
The addition of tier 0 storage to the storage hierarchy presents a paradigm shift. It represents a change from simply moving less active data to slower, less expensive storage to focusing on efforts to move more active data to faster, more expensive storage.
Here is an example of what an imaginary storage hierarchy that incorporates tier 0 might look like:
|0||Transactional data requiring extremely high performance||SLC solid-state storage|
|1||Mission-critical application data||Fibre Channel Storage Area Network (SAN) or SAS HDDs|
|2||Less-critical data that could be recovered after mission-critical application data||SATA disks arrays|
|3||Data that is seldom used||CD-R or tape|
|4||Archived email retained for compliance||Public cloud|