Hybrid array

A hybrid array is a form of hierarchical storage management that combines hard disk drives (HDDs) with solid-state drives (SSDs) for I/O speed improvements.

Hybrid storage arrays aim to mitigate the ever increasing price-performance gap between HDDs and DRAM by adding a non-volatile flash level to the memory hierarchy. Hybrid arrays thus aim to lower the cost per I/O, compared to using only SSDs for storage. Hybrid architectures can be as simple as involving a single SSD cache for desktop or laptop computers, or can be more complex as configurations for data centers and cloud computing.

Implementations
Some commercial products for building hybrid arrays include:
 * Adaptec demonstrated the MaxIQ series in 2009.
 * Apple's Fusion Drive
 * Linux software includes bcache, dm-cache, and Flashcache (and its fork EnhanceIO).
 * Condusive's ExpressCache is marketed for laptops.
 * EMC Corporation VFcache was announced in 2012.
 * Fusion-io acquired ioTurbine in 2011, and the product line it acquired by buying NexGen in 2013.
 * Hitachi Accelerated Flash Storage (HAFS) used together with the Hitachi Dynamic Tiering software
 * IBM Flash Cache Storage Accelerator (FCSA) server software
 * Intel's Smart Response Technology for desktop
 * Intel's Cache Acceleration Software for servers and workstations
 * LSI CacheCade software for their controllers
 * Marvell's HyperDuo controllers
 * Microsoft's Automated Tiering (since Windows 2012 R2)
 * NetApp's Flash Cache, Flash Pool, Flash Accel
 * Oracle Corporation markets products such as Exadata Smart Cache Flash, and the FS1 flash storage system.
 * Microsoft ReadyBoost allows personal computers to USB flash drives as cache.
 * Nvelo DataPlex SSD caching software was announced in 2011, and was acquired by Samsung in 2012.
 * SanDisk FlashSoft for Windows, Linux, and vSphere
 * Products are offered by vendors like AMI StorTrends, Tegile Systems, Reduxio, and Tintri.
 * ZFS using hybrid storage pools, are used for example in some Oracle Corporation products.