A flash array is a solid state storage disk system that contains multiple flash memory drives instead of hard disk drives.
Major storage vendors began sell flash in their arrays in 2008 as solid state drive (SSD) RAID replacing a limited amount of hard drives, or as PCI Express (PCIe) cards in the array alongside hard drives. Flash memory transfers data to and from SSDs much faster than electromechanical disk drives transfer data, reducing seek time and latency. However, flash is far more expensive than spinning disk. There were other early hurdles to adoption, including lack of software for placing only data that requires peak performance on the expensive SSDs. Also, array controllers built for spinning disk failed to take full advantage of flash’s performance.
Smaller vendors such as Nimbus Data Systems, Pure Storage and SolidFire began selling systems with all-flash drives in 2010 and 2011, engineering those arrays specifically for SSDs. These systems included management software with features such as data deduplication and thin provisioning at a per-gigabyte price comparable or even below hard drive arrays. Other vendors have more expensive all-flash arrays designed for the highest performance needs in the enterprise.
Most major storage vendors have developed sub-volume tiering software that efficiently places data on the right storage tier – usually flash for highest performance and low-cost, high capacity SAS or SATA drives for less frequently accessed data.
The development of multi-level cell (MLC) flash has also lowered the price of SSDs. MLC flash is slower and less durable than single-level cell (SCL) flash, but companies have developed software that improves its wear levels to the point where MLC is acceptable for enterprise application. SLC flash remains the choice for applications with the highest I/O requirements, however.
NAND flash is the main type used for storage systems, although other types of flash such as phase-change memory (PCM), magnetoresistive RAM (MRAM) and resistive RAM (RRAM). are expected to eventually replace NAND in enterprise storage arrays.