It May No Longer Be NAS Versus SAN


Networked storage will continue to see a truce, if not a nice cooperative friendship, between storage area networks (SAN) and network-attached storage (NAS) devices - two different methods of attaching storage and servers.

For the past several years, the trade press, however, has produced tons of articles about the distinct differences between NAS devices and SANs. These days trade press articles focus more on NAS devices and SANs being complementary solutions for different storage needs and, and as a result of this, starting to converse.

It all comes down to the bottom line - how and for what purpose does the information, which that lives on the storage device, and the application, which lives on the server, need to be move, managed, enhanced, and presented.

SANs emerged in the mid-1990s as a way to consolidate islands of server-bound storage. The idea consisted of freeing the servers to do what they do best - process data - while housing information in a central location. Here the data can be managed, protected, and share. SANs also reduce bulk of server-to-server data movement that has been clogging LANs for years.

SANs also optimize the speed of processing reads and writes for applications, such as databases, and data warehousing, that require quick movement between storage and server.

SANs have come about largely because of the Fibre Channel network interconnection technology. A combination of industry-standard cabling hardware and software protocols, Fibre Channel provides the capability to use switches to interconnect multiple servers with multiple storage systems. This technique enables an IT department to use familiar channel I/O-based technology to build a fabric topology -- one that connects many storage elements with many computer systems. To this end, SANs can now provide access to any storage system from any host or servers, thus making better use of the storage assets and having them managed by fewer IT personnel.

NAS devices, on the other hand, use the maturity and ubiquity of IP-based networks to provide access to stored information. While SANs provide channel topologies to deliver large, block-level data to servers, NAS devices enable many users to access individual files at the same time. NAS devices have become ideal for serving Web pages to 1,000's of workstations at the same time. NAS devices have become popular in CAD/CAM environments where engineers have to share design drawings. NAS devices appear like another network drive a workstation can access.

To leverage the existing IP network for this purpose, NAS devices use special file-serving protocols, such as NFS for Unix and CIFS for Windows NT. These protocols enable the servers to communicate efficiently with a file server.

By managing the file system centrally, NAS devices enable multiple workstations to access single files at the same time. The capability makes NAS devices well suited for applications and environment requiring a great deal of file sharing among multiple hosts or clients, even if they have different operating systems.

Both NAS devices and SANs offer both advantages and disadvantages. On the other hand, an enterprise storage infrastructure can require both NAS devices and SANs. For example, an organization can use NAS devices for Web servers and network-shared directories, and, at the same time, have SANs for client/server and database applications. In some cases, the NAS file server can be connected to the storage on a SAN.

Further, storage networking solutions that use multipath file-serving (MPFS) software leverage the best of both SANs and NAS devices for use in a traditional NAS application. Using MPFS software, large-volume NAS-based data can be sent over a SAN channel to a host. This technique avoids the performance decrease that may occur in an IP network when large files get transferred.

Although solutions like MPFS allow SANs and NAS devices to converge, an IT department has to consider what's the most productive way to use these two network storage solutions - separately or combined.


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