The term secondary storage can have a few meanings, depending on its context.
Computer storage is almost always hierarchical, and is made up of primary and secondary storage. Primary storage typically refers to random access memory (RAM) placed near the computer’s CPU to reduce the amount of time it takes to move data between the storage and CPU.
Secondary storage (sometimes referred to as secondary memory) is at the lower level of the storage hierarchy. It commonly refers to hard disk drives (HDDs), solid-state drive (SSD) storage (flash) or other types of storage devices.
Computers use primary and secondary storage for a number of reasons:
- RAM-based storage is volatile. This means RAM contents are not kept when the power is turned off. In contrast, non-volatile storage devices such as HDDs and SSDs retain their contents even without power.
- RAM is far more expensive than non-volatile storage on a cost-per-gigabyte basis. The tradeoff is that primary storage (RAM) is much faster than secondary storage. A combination of primary and secondary data allows the computer to take advantage of high-speed, low-capacity, volatile storage and high-capacity, relatively low-speed, non-volatile storage.
When primary storage refers to local disks installed inside the server’s chassis or to disks in an external storage array, secondary storage may refer to offline or remote storage (such as optical media, a backup tape or a remote archive).
Secondary storage typically provides high capacity, but the data may not be immediately accessible. A backup server, for example, may contain vast quantities of data, but the data set is only accessible through dedicated backup software, not through file-level read operations. Similarly, secondary storage media such as optical disks and backup tapes must be mounted before they can be read.
Secondary storage can also refer to cloud storage. This is especially true when cloud storage is used for data archiving. Many organizations find cloud-based archives to be a more cost-effective way to store aging, relatively static data than locally on a server’s primary storage.
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What kinds of secondary storage devices do you use in your organization?
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