What About NAS?

While SANs are networks that connect storage to servers, think of a NAS as a server with a lot of local storage.

Network Attached Storage (NAS) is much different from SANs. While SANs are networks that connect storage to servers, think of a NAS as a server with a lot of local storage. A NAS can have up to several terabytes of local storage and includes a scaled-down operating system. Popular NAS OSs include Linux and even Windows 2000 Server (minus several non-storage-related services).

Because a NAS includes an OS, many consider it to be an appliance you just plug into your network. Just like buying a new refrigerator—buy it, bring it home and plug it in! When you need more storage, add disks to the NAS or just buy another NAS. When you purchase a NAS, you’re buying a pure file server that’s ready to go out of the box—literally.

NAS boxes also come with a “break-me-if-you-can” attitude at no extra charge. Some NAS boxes have pretty much “redundant everything” included (disks, power supply, network and so on), morphing the dream of 99 percent data availability into reality.

To eliminate any confusion, the table below outlines the key differences between NAS and SAN.

Decision Point SAN NAS
Data Access • Block level (fast) • Fast data access
Data Security • Not connected to LAN
• Zoning limits access to physical SAN resources
• File level (slower)
• Available to devices connected to LAN
Deployment • Complex • Easy
Fault tolerance • Achieved through proper planning of SAN architecture (Redundant switches, storage arrays and so on) • Fault-tolerant hardware built into many NAS devices
Management • Local to SAN switches or performed at the enterprise level with SAN management software • Local to NAS box via NAS management software

• Distributed and redundant storage applications
• Block-level backup and recovery ability

• Accessible file storage, server consolidation

Another difference between SAN and NAS is in the area of applications. Server applications see storage on the SAN as local storage, so it’s easy to install and configure applications to use SAN resources. Because many NAS boxes are built as appliances, you can’t install applications on them. While, from a stability perspective, no applications on the filer should mean high degree of uptime, this philosophy also limits how and where the filer can be used on your network.

Many NAS devices have SCSI or even fibre channel HBAs, allowing them to access storage and libraries on a SAN. Because of NAS vendors’ willingness to add fibre channel HBAs to their NAS boxes, NAS shouldn’t be looked at as an alternative to SAN, but rather as a complement. For backup and recovery purposes, backing up NAS devices to a library attached to the SAN offers the best in performance and scalability. The alternatives to this approach are to dedicate a library or tape drive to the NAS box or back up the NAS box over the local area network.

About the Author

Chris Wolf is VMware's CTO, Global Field and Industry.


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