Disk array

A disk array is a disk storage system which contains multiple disk drives. It is differentiated from a disk enclosure, in that an array has cache memory and advanced functionality, like RAID and virtualization.

Components of a typical disk array include:

• Disk array controllers
• Cache memories
• Disk enclosures
• Power supplies

Typically a disk array provides increased availability, resiliency and maintainability by using additional, redundant components (controllers, power supplies, fans, etc.), often up to the point when all single points of failure (SPOFs) are eliminated from the design. Additionally those components are often hot-swappable.

Typically, disk arrays are divided into five categories: NAS, Modular SAN arrays, Monolithic SAN arrays, Storage Virtualization and Utility SAN Arrays.

Network attached storage (NAS) arrays

Network attached storage is a hard disk storage system on a network with its own LAN IP address. NAS arrays provide file-level access to storage through such protocols as CIFS and NFS. Examples:

• 3PAR and ONStor UtiliCat Unified Storage
• EMC Celerra family
• HP StorageWorks All-In-One Storage Systems
• HP ProLiant Storage Server
• NetApp Filer
• Sun StorageTek 5000 family

Modular storage area network (SAN) arrays

A SAN is a dedicated network, separate from LANs and WANs, that is generally used to connect numerous storage resources to one or many servers. SAN arrays provide block-level access to storage through SCSI-based protocols such as Fibre Channel and iSCSI. Modular storage system typically consist of separate modules, which afford some level of scalability, and can be mounted in a standard rack cabinet. Modular storage systems are also sometimes referred as departmental. Examples:

• 3PAR InServ E-Class
• EMC CLARiiON
• Fujitsu ETERNUS 4000/3000 series storage arrays
• HP Storageworks EVA family products
• Hitachi WMS & AMS family products
• IBM DS4000/FAStT family of storage servers
• IBM DS6000 series storage servers
• Arena Maxtronic Janus Fibre Channel and iSCSI RAID systems
• Infortrend EonStor/EonRAID family
• NetApp FAS series Unified storage servers
• ONStor Pantera
• Sun StorageTek 6x40
• Xiotech Magnitude 3D

Monolithic (enterprise) arrays

Although this is not a strict definition, the array is considered monolithic when even basic configuration is physically too large to fit into a standard rack cabinet. These arrays are suited for large-scale environments. Often Enterprise storage systems provide ESCON and FICON protocols for mainframes in addition to Fibre Channel and iSCSI for open systems SANs. Examples:

• EMC Symmetrix
• Fujitsu ETERNUS 8000/6000 series storage arrays
• Hitachi Lightning and TagmaStore USP family products
• HP XP(OEM'd from Hitachi)
• IBM Enterprise Storage Server (ESS)
• IBM DS8000 series of storage servers
• Infortrend EonStor / EonRAID family
• Sun StorEdge 99xx (9970, 9980, 9985, 9990 OEM's from Hitachi))

Storage virtualization

Intelligent SAN or Storage Servers (Software that adds disk controller functionality to standard server hardware platforms). Hardware independent software that typically runs as a control program on top of a standard OS platform (Windows, Linux, etc.):

• DataCore Software Corporation SANsymphony and SANmelody Storage Server Virtualization Software
• Falconstor IPStor Software
• IBM SAN Volume Controller
• NetApp V-Series storage virtualization solutions
• RELDATA Unified Storage Gateway Appliance
• EMC inVista
• Hitachi Universal Storage Platform Controller

Utility Storage arrays:

• 3PAR InServ Storage Servers
• NetApp FAS GX Series
• Pillar Data Systems Axiom