NAS – network attached storage

Network-attached storage uses a standard Ethernet connection to provide network nodes with file-based shared storage services. Most have a Linux-based OS.
NAS devices, which typically do not have a keyboard or display, are configured and managed with a Web-based utility program. Each NAS resides on the LAN as an independent network node and has its own IP address.
An important benefit of NAS is its ability to provide multiple clients on the network with access to the same files.
Some higher-end NAS products can hold enough disks to support RAID.
Communication with a NAS head occurs over TCP/IP. The two application protocols most commonly associated with NAS are Sun Network File System (NFS) and Common Internet File System (CIFS, ranije poznat kao Server Message Block ili SMB). Many NAS systems also support Hypertext Transfer Protocol (HTTP). Clients can often download files in their Web browser from a NAS that supports HTTP.
Uređaj se obično naziva NAS head ili NAS box.

High-end or enterprise NAS: The high end of the market is driven by businesses that need to store huge amounts of files, including virtual machine (VM) images. High-end NAS provides rapid access and NAS clustering capabilities.
Midmarket NAS: This end of the market can accomodate businesses that require several hundred terabytes of data. Midmarket NAS devices cannot be clustered, however, which can create file-system siloes when multiple NAS devices are required.
Low-end or desktop NAS: The low end of the market is aimed at small businesses and home users who require local shared storage. Increasingly, this market is shifting toward a cloud NAS model.

Dobar link za opšte stvari o NAS uređajima, i za poređenja sa SAN-ovima i DAS-ovima.
Koje su firme na tržištu NAS-ova : Hitachi, NetApp, Dell, EMC, HP, Oracle, IBM (navedene bez nekog posebnog reda).

Osnovne karakteristike na koje treba obratiti pažnju kod NAS uređaja (dobar link) :
Kapacitet – obično su u uređaju SATA diskovi, ali ih ima i sa SSD diskovima. Neki imaju USB i/ili iSCSI za proširenje kapaciteta. Paziti takođe koja se verzija SATA diskova nudi (II-300Mb/s ili III-600Mb/s bandwidth throughput).
Konektivnost – treba da ima Gigabit Ethernet, i to dve ili više kartica (port trunking, port aggregation). Postoji opcija i sa wireless povezivanjem.
Performanse – povećavaju se sa bržim procesorima i/ili memorijom. Visoko performantni NAS-ovi imaju i po 8G RAM-a, i Intel Core i3 procesore. Jeftiniji NAS uređaji imaju Marvell čipove.
Backup&Recovery – RAID je obavezan, kao i hot-swap diskovi (zamena bez isključivanja uređaja). Paziti jer dosta NAS-ova imaju samo JBOD (just a bunch of disks, dakle bez RAID-a). Takođe treba raditi i redovan bekap konfiguracije samog NAS uređaja.
Security – neki uređaji podržavaju enkripciju, firewall, a tu su i fizički lokoti za vezivanje za zid i naravno user+pass autentifikacija.

Link za poređenje nekoliko uređaja srednjeg nivoa (od sredine 2014.).

Neke karakteristike koje su bitne :
SATA – Serial ATA diskovi. Razlike postoje i u “gnezdima” za diskove i u samim diskovima. Pre SATA standarda koristili su se IDE diskovi.
SATA II – javlja se od 2006 godine, peak trasfer rate 3 Gbps. Novo ime je SATA 3.0
SATA III – javlja se od decembra 2012 godine, peak trasfer rate 6 Gbps. SATA II disk se može staviti u SATA III port i radiće normalno. Novo ime za SATA III je SATA 6.0
USB – kabliranje između 2.0 i 3.0 je različito (4 odnosno 8 žica u kablu)
USB 2.0 – od 2000, brzina je 480 Mbps, 4 žičice
USB 3.0 – od novembra 2008, brzina je 4.8 Gbps, 8 žičica