Calculating Memory

You can calculate memory according to general or specific memory rules.

General Memory Rules

Follow these general guidelines to calculate the amount of memory you will need.

• Virtual memory = RAM (main memory) + swap space

• Calculate the amount of memory according to the five-minute rule:

Memory is sized at 16 Mbytes plus memory to cache the data, which will be accessed more often than once in five minutes.

Specific Memory Rules

Follow these specific guidelines to calculate the amount of memory you will need.

• If your server primarily provides user data for many clients, configure relatively minimal memory.

For small installations, this will be 32 Mbytes; for large installations, this will be about 128 Mbytes. In multiprocessor configurations, provide at least 64 Mbytes per processor. Attribute-intensive applications normally benefit slightly more from memory than data-intensive applications.

• If your server normally provides temporary file space for applications that use those files heavily, configure your server memory to about 75 percent of the size of the active temporary files in use on the server.

For example, if each client's temporary file is about 5 Mbytes, and the server is expected to handle 20 fully active clients, configure it as follows:

(20 clients x 5 Mbytes)/75% = 133 Mbytes of memory

Note that 128 Mbytes is the most appropriate amount of memory that is easily configured.

• If the primary task of your server is to provide only executable images, configure server memory to be equal to approximately the combined size of the heavily-used binary files (including libraries).

For example, a server expected to provide /usr/openwin should have enough memory to cache the X server, CommandTool, libX11.so, libview.so and libXt. This NFS application is considerably different from the more typical /home, /src, or /data server in that it normally provides the same files repeatedly to all of its clients and is hence able to effectively cache this data. Clients will not use every page of all of the binaries, which is why it is reasonable to configure only enough to hold the frequently-used programs and libraries. Use the cache file system on the client, if possible, to reduce the load and RAM needs on the server.

• If the clients are DOS PCs or Macintosh machines, add more RAM cache on the Sun NFS server; these systems do much less caching than UNIX system clients.