[1] In a typical HSM scenario, data which is frequently used are stored on warm storage device, such as solid-state disk (SSD).
Data that is infrequently accessed is, after some time migrated to a slower, high capacity cold storage tier.
In practice, HSM is typically performed by dedicated software, such as IBM Tivoli Storage Manager, or Oracle's SAM-QFS.
HSM is often used for deep archival storage of data to be held long term at low cost.
Automated tape robots can silo large quantities of data efficiently with low power consumption.
Some HSM software products allow the user to place portions of data files on high-speed disk cache and the rest on tape.
More precisely, the policy decides which tier a file should be stored in, so that the entire storage system can be well-organized and have a shortest response time to requests.
[5] While tiering solutions and caching may look the same on the surface, the fundamental differences lie in the way the faster storage is utilized and the algorithms used to detect and accelerate frequently accessed data.
[7][6] The basic idea is, mission-critical and highly accesses or "hot" data is stored in expensive medium such as SSD to take advantage of high I/O performance, while nearline or rarely accessed or "cold" data is stored in nearline storage medium such as HDD and tapes which are inexpensive.