Displaying Server Preference Ranks

Displaying Server Preference Ranks
	Chapter 3. Displaying Information about OpenAFS

The Cache Manager stores a list of preference ranks for file server machines. When it needs to access a file or directory, the Cache Manager compares the ranks of the file server machines that house the relevant volume. It first tries to access the volume on the machine with the best rank. (If a file server machine is multihomed--has more than one network interface--the Cache Manager actually assigns a separate rank to each interface.)

The Cache Manager assigns a default rank to a file server machine interface by comparing its own IP address to the interface's IP address. It assigns a better rank to interfaces that are on its own subnetwork or network than to interfaces on other networks. Therefore, the ranks bias the Cache Manager to fetch files from file server machines that are close in terms of network distance, which tends to reduce network traffic and help the Cache Manager deliver data to applications more quickly.

The Cache Manager stores each rank as a pairing of a file server machine interface's IP address and an integer rank from the range 0 to 65,534. A lower number is a better rank. To display the server preference ranks on the local client machine, use the fs getserverprefs command.

The Cache Manager stores a separate but similar set of ranks for Volume Location (VL) Servers, which tell the Cache Manager the location of volumes that house files and directories. To display those ranks, add the -vlservers flag to the fs getserverprefs command.

If the default ranks do not seem to result in the best performance, your system administrator can change them. Ask your system administrator about the ranks if appropriate.

To Display Server Preference Ranks

Issue the fs getserverprefs command to display the file server machine preference ranks used by the Cache Manager on the local machine. To display VL Server ranks, add the -vlservers flag. By default, the Cache Manager has the IP address of each interface translated into a hostname before displaying it. To bypass the translation and display IP addresses, include the -numeric flag. This can significantly speed up the command's output.

   % fs getserverprefs [-numeric] [-vlservers]

The following example displays the file server machine preference ranks for a client machine in the example.com cell. The ranks of the file server machines in that cell are lower than the ranks of the file server machines from the foreign cell, example.net. Because the -numeric flag is not used, the output displays hostnames. The appearance of an IP address for two machines indicates that translating them was not possible.

   % fs getserverprefs
   fs2.example.com           20007
   fs3.example.com           30002
   fs1.example.com           20011
   fs4.example.com           30010
   server1.example.net       40002
   192.12.105.34             40000
   server6.example.net       40012
   192.12.105.37             40005


Determining Access to Foreign Cells		Chapter 4. Protecting Your Directories and Files