Network Appliance uses the term news cache to describe a NetCache appliance that is configured to provide news caching service for news servers that support the Network News Transport Protocol (NNTP). A news cache requests news data from a news server on behalf of a client and caches that data. The news cache and news server communicate through NNTP.
A news cache might also be configured for DNS caching.
The following illustration shows the flow of a news request from the client to the news server by way of the news cache and from the news server back to the client.
In NNTP news transport, the primary role of news servers is to receive news from and send news to other news servers. One news server creates a connection to a downstream news server and offers news to that server. The downstream server responds as to whether the upstream server should send particular articles. News servers routinely accept very large news feeds from other servers, which requires an administrator to closely monitor disk usage on the news storage device.
The news cache, however, cannot accept a news feed. It receives news only when it establishes a connection to the news server. If a client requests an article that is not in the news cache, the news cache initiates a connection to the news server to fetch the article. As shown in the previous illustration, the fetched article is returned to the client and is cached by the news cache.
A NetCache news cache can connect to only one news server. Multiple news caches can connect to the same news server, however.
Including a news cache in your news environment can have the following benefits:
If news clients have been connecting to a server over a WAN, deploying a news cache close to the clients reduces traffic over the WAN. The reason is that multiple requests for the same news data can be fulfilled by the cache rather than having to send each request across the WAN to the news server.
Without a news cache, each client would open a TCP/IP connection to the news server for every news session, resulting in a high volume of traffic over the WAN.
Even in the case of cache misses, you save bandwidth by deploying a news cache. The cache can send many cache misses over a connection that it establishes with the news server. TCP/IP setup is not necessary for each cache miss.
If you deploy a news cache close to your clients, you can provide news more quickly to your users.
For some NetNews software, a point is reached at which you cannot easily expand the news server to handle more news requests. Deploying a news cache can significantly reduce the server resources required for a given number of clients. The reason is that a news cache can handle many hundreds of connections, whereas Reader servers typically can handle only a small number of connections.
Note
A Reader server is the component of the news server that handles client connections for news. The Reader server software might be installed on the same computer as other news server components, or it might be on a dedicated computer.
Requests for the same article are handled more efficiently by a news cache than by some news servers. For some news servers, it is "expensive" to handle multiple requests for the same article. The reason is that each time a client requests an article, a news server must perform a lookup through its entire directory structure.
A news cache does not accept or send news feeds. Therefore, a news cache administrator does not have to closely monitor disk usage, as is necessary for a news server. Nor does the administrator need to manage any issues in regard to the news cache's interaction with news servers. After you configure your news caches, administration of the news caches is minimal.
To deploy a NetCache appliance as a news cache, you must obtain a license from Network Appliance for NNTP.
The most widely deployed news server software requires approximately 1 MB per client connection. Taking file system buffers, the operating system, and other overhead into consideration, a Reader server with 1 GB of memory might struggle to handle about 500 client connections. NetCache is far more efficient. Using similar hardware, NetCache can handle thousands of client connections. With a news cache deployed, significantly fewer connections to the news server are required because NetCache can resolve duplicate requests from the cache.
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Part No. 210-00372
File: nntpdpl2.htm
Last updated: 11/13/02 18:11:44