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Using SANs and NAS by W. Curtis Preston

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System Architecture Advances

Although significant advancements have been made in the protocols themselves, many believe that the greatest performance enhancements have come from creating filers designed from the ground up to be dedicated entirely to serving network-mounted filesystems via NFS or CIFS. (Early filers did not support CIFS, but all major NAS vendors do today.)

Tip

No single NAS vendor has implemented all the advances discussed here. In fact, there are vendors that have implemented none of these enhancements. Ask your NAS vendor what they have done to improve performance and reliability.

To understand the architectural improvements NAS vendors have made, we must first look at how traditional NFS and CIFS services are provided. Historically, such services were available only by using the appropriate software on a Unix or Windows server. Unix servers served NFS volumes, and Windows servers served CIFS volumes. One of the problems with this design is that a dedicated server was not required. This often meant that NFS and CIFS volumes were served by a machine that had many other tasks.

Even a dedicated NFS or CIFS server was required to do quite a bit of work to process a single NFS or CIFS request. A look at Figure 5-1 should help illustrate this. Each request is received on one of the server's network interface cards, or NICs, in the form of network packets. This request must then be processed by the appropriate network layer software, such as TCP/UDP and IP. Once the ...

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