Hybrid drive

In computing, a hybrid drive is a logical or physical storage device that combines a fast storage medium such as NAND flash solid-state drive (SSD) with a hard disk drive (HDD), with the intent of adding some of the speed of flash storage to the cost-effective storage capacity of traditional HDDs. The purpose of the SSD in a hybrid drive is to act as a cache for the data stored on the HDD, improving the overall performance by keeping copies of the most frequently used data on the faster SSD.

There are two main configurations for implementing hybrid drives: dual-drive hybrid systems and solid-state hybrid drives. In dual-drive hybrid systems, physically separate SSD and HDD devices are installed in the same computer, having the data placement optimization performed either manually by the end user, or automatically by the operating system through the creation of a "hybrid" logical device. In solid-state hybrid drives, SSD and HDD functionalities are built into a single piece of hardware, where data placement optimization is performed either entirely by the device (self-optimized mode), or through placement "hints" supplied by the operating system (host-hinted mode).

There are two main "hybrid" storage technologies that combine NAND flash memory or SSDs, with the HDD technology: dual-drive hybrid systems and solid-state hybrid drives.

Dual-drive hybrid systems combine the usage of separate SSD and HDD devices installed in the same computer. Overall performance optimizations are managed in one of three ways:

Solid-state hybrid drive (also known by the initialism SSHD) refers to products that incorporate a significant amount of NAND flash memory into a hard disk drive (HDD), resulting in a single, integrated device. The term SSHD is a more precise term than the more general hybrid drive, which has previously been used to describe SSHD devices and non-integrated combinations of solid-state drives (SSDs) and hard disk drives. The fundamental design principle behind SSHDs is to identify data elements that are most directly associated with performance (frequently accessed data, boot data, etc.) and store these data elements in the NAND flash memory. This has been shown to be effective in delivering significantly improved performance over the standard HDD.

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