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
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.
||• Block level (fast)
||• Fast data access
||• Not connected to LAN
• Zoning limits access to physical SAN resources
|• File level (slower)
• Available to devices connected to LAN
||• Achieved through proper planning
of SAN architecture (Redundant switches, storage arrays
and so on)
||• Fault-tolerant hardware built
into many NAS devices
||• Local to SAN switches or performed
at the enterprise level with SAN management software
||• Local to NAS box via NAS management
• Distributed and redundant storage applications
• Block-level backup and recovery ability
|• Accessible file storage, server
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.
Chris Wolf is VMware's CTO, Global Field and Industry.