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Introduction to network attached storage

(NAS)

While aSANovercomes these problems,Fibre Channelcomponents and management tools canbe too expensive and too complex for basic network storage tasks.Network attached storage

(NAS)offers accessibility and performance that falls between server storage and SAN storage.

Traditional NAS devices attach to theLANthrough an ordinary Ethernet connection and IP

address, providing disk storage as an independent network device (although NAS devices can

also be added to a SAN). Multiple NAS "boxes" can be added to the LAN as needed for

additional network storage.

NAS hardware and architecture

A NAS box is a dedicated storage server that includes a NAS head and disk drives that areattached to a network. The NAS head (aka NAS front end or NAS gateway) is the control

electronics that interface the network and storage. A basic NAS may use just one head or share

the internal storage across multiple heads to accommodate increased network bandwidth.

In terms of storage, NAS systems are denoted by their drive support, the total number of drives

and the total capacity. SATA drives are by far the most common type of drive in NAS systems.

SATA drives allow for low-cost high-density NAS storage,

althoughATA,SCSI,SATAandSASdrives also also used. Even Fibre Channel (FC) drives can be

used in high-end NAS models.

Workgroup-type NAS systems support 1 TB to 2 TB of disk storage (or more) with a small group

of four to six hard disks, depending on the model and options selected. (Some models support

expansion disk racks that allow extended storage up to 30 TB.) Enterprise-class NAS systems

can implement many disks and offer capacities well over 100 TB. Most NAS systems include

RAID support for data protection and can implement common RAID levels, including RAID 0,

RAID 1, RAID 5 and RAID 6/DP. NAS systems also include some onboard memory (RAM)

tocachenetwork data to or from the disks. Small NAS devices may only provide a 128 MB to

256 MB cache, though enterprise-class NAS systems may offer cache up to 4 GB.

A NAS box must actually connect to the LAN, so the network interface is also important. Gigabit

Ethernet (GigE) ports are almost universal and 10 Gigabit Ethernet interfaces are on thehorizon. Some NAS products provide multiple Ethernet connections for network interface

aggregation, redundancy or failover.

As an example, consider the V800 workgroup NAS system from Mpak Technologies. The V800

supports up to eight ATA disks in RAID configurations to level 5. The unit includes up to 512 MB

of cache and offers two 10/100 Ethernet ports (GigE ports are an option). By comparison, the

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StorEdge 5310 NAS from Sun Microsystems Inc. natively supports 18 disks up to 2.6 TB and 4 GB

of onboard cache, and includes two 10/100/1000 Ethernet ports for connectivity.

While NAS boxes typically work independently, they can also be aggregated intoclusters.

Similar in principle to clustered computing, NAS clusters appear to the LAN as a single NAS

device. Each clustered element can share the data load and each box in the cluster can providefailover if another box fails, improving storage performance and achieving high storage

availability. OnStor Inc. provides a clustered NAS gateway designed to interconnect Windows,

Linux and Unix client systems with up to 40 PB of storage capacity from a variety of vendors.

NAS protocols

Protocols are sets of rules that define the way that two end points communicate. NAS devices

interact with the LAN using various protocols that manage activities like networking, file

exchanges and applications.

Networking protocols include Novell Inc.'sIPXand Microsoft'sNetBEUI. NAS devices can share

and exchange files using recognized file protocols like Sun'sNFSor theCIFSopen standard

based on Microsoft's Server Message Block (SMB) protocol. CIFS complements existing Internet

application protocols like theFTPandHTTP. For example, Sun's StorEdge 5310 NAS includes

support for CIFS/SMB, NetBIOS, NFS v2 and v3, and FTP.

NAS management

NAS devices typically run their own proprietary operating system, and are managed and

configured using integrated software utilities that run across any standard Web browser. This

allows storage administrators to check NAS status, diagnose issues and make changes to the

NAS configuration from any workstation on the LAN. Any management tool(s) should include

support for the NAS boxes on your LAN -- including discovery -- and should present detailed

information through a single console. NAS devices frequently include utilities to tackle tasks

such as snapshot, replication or backup. When evaluating a NAS product, it's important to test

the utilities included with the unit to ensure that the software will behave properly on your

network.

Every NAS box will absolutely require some amount of routine management work, but NAS

management overhead is cumulative. As more NAS boxes appear on the LAN, or even the SAN,

more management time is required. Eventually, this can strain limited IT staff.

NASvirtualizationis one way to deal with management overhead. The same virtualization

technologies that can treat a variety of storage resources as a single pool of storage can also be

applied to NAS devices -- locating, identifying and combining NAS resources so that they can be

treated and managed as a single entity (ideally through a single management console).

Dedicated NAS virtualization appliances are typically installed between NAS boxes and the

network.

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NAS backup

Today's tighter backup windows and shrinking recovery objectives are forcing storage

administrators to rethink their tape backup strategies. Disk storage is displacing tape as

abackupmedium for its enhanced speed, RAID data protection features and cost-effectiveness.

These features, combined with ease of installation, are making NAS devices attractive backuptargets.

Although any NAS box can be used for backups, some NAS appliances are dedicated to backup

tasks. The NearStore system from NetApp is designed for nearline storage from 8 TB to 96 TB

using inexpensive SATA disks. When employing a NAS system as a backup target, be sure your

backup software supports the network data management protocol (NDMP). Backup software

should also be compatible with the version of NDMP in use. More information is available

about the NDMPhere.

While NAS may provide an attractive backup target for some applications, remember that NASdoes not replace tape backups completely. Disk space is finite, and NAS systems will eventually

fill with backup data, forcing older backups to be deleted or offloaded to tape. Disk storage also

remains on-site, so organizations relying on tape for off-site disaster protection may need to

continue periodic tape backups.

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