dm-cache is a component (more specifically, a target) of the Linux kernel's device mapper, which is a framework for mapping block devices onto higher-level virtual block devices. It allows one or more fast storage devices, such as flash-based solid-state drives (SSDs), to act as a cache for one or more slower storage devices such as hard disk drives (HDDs); this effectively creates hybrid volumes and provides secondary storage performance improvements.

The design of dm-cache requires three physical storage devices for the creation of a single hybrid volume; dm-cache uses those storage devices to separately store actual data, cache data, and required metadata. Configurable operating modes and cache policies, with the latter in the form of separate modules, determine the way data caching is actually performed.

dm-cache is licensed under the terms of GNU General Public License (GPL), with Joe Thornber, Heinz Mauelshagen and Mike Snitzer as its primary developers.

dm-cache uses solid-state drives (SSDs) as an additional level of indirection while accessing hard disk drives (HDDs), improving the overall performance by using fast flash-based SSDs as caches for the slower mechanical HDDs based on rotational magnetic media. As a result, the costly speed of SSDs becomes combined with the storage capacity offered by slower but less expensive HDDs. Moreover, in the case of storage area networks (SANs) used in cloud environments as shared storage systems for virtual machines, dm-cache can also improve overall performance and reduce the load of SANs by providing data caching using client-side local storage.

dm-cache is implemented as a component of the Linux kernel's device mapper, which is a volume management framework that allows various mappings to be created between physical and virtual block devices. The way a mapping between devices is created determines how the virtual blocks are translated into underlying physical blocks, with the specific translation types referred to as targets. Acting as a mapping target, dm-cache makes it possible for SSD-based caching to be part of the created virtual block device, while the configurable operating modes and cache policies determine how dm-cache works internally. The operating mode selects the way in which the data is kept in sync between an HDD and an SSD, while the cache policy, selectable from separate modules that implement each of the policies, provides the algorithm for determining which blocks are promoted (moved from an HDD to an SSD), demoted (moved from an SSD to an HDD), cleaned, etc.

When configured to use the multiqueue (mq) or stochastic multiqueue (smq) cache policy, with the latter being the default, dm-cache uses SSDs to store the data associated with performed random reads and writes, capitalizing on near-zero seek times of SSDs and avoiding such I/O operations as typical HDD performance bottlenecks. The data associated with sequential reads and writes is not cached on SSDs, avoiding undesirable cache invalidation during such operations; performance-wise, this is beneficial because the sequential I/O operations are suitable for HDDs due to their mechanical nature. Not caching the sequential I/O also helps in extending the lifetime of SSDs used as caches.

Another dm-cache project with similar goals was announced by Eric Van Hensbergen and Ming Zhao in 2006, as the result of an internship work at IBM.

Later, Joe Thornber, Heinz Mauelshagen and Mike Snitzer provided their own implementation of the concept, which resulted in the inclusion of dm-cache into the Linux kernel. dm-cache was merged into the Linux kernel mainline in kernel version 3.9, which was released on April 28, 2013.