Managing NFS and NIS, 2nd Edition - Mike Eisler [65]
noac
This option suppresses attribute caching and forces writes to be synchronously written to the NFS server. The purpose behind this option to is let each client that mounts with noac be guaranteed that when it reads a file from the server it will always have the most recent copy of the data at the time of the read. We will discuss attribute caching and asynchronous/synchronous NFS input/output in more detail in Chapter 7.
actimeo=n
The options that have the prefix ac(collectively referred to as the ac* options)affect the length of time that attributes are cached on NFS clients before the client will get new attributes from the server. The quantity n is specified in seconds. The two options prefixed with acdiraffect the cache times of directory attributes. The two options prefixed with acreg affect the cache times of regular file attributes. The actimeo option simply sets the minimum and maximum cache times of regular files and directory files to be the same. We will discuss attribute caching in more detail in Chapter 7.
* * *
Tip
It is a popular misconception that if the minimum attribute timeout is set to 30 seconds, that the NFS client will issue a request to get new attributes for each open file every 30 seconds. Marketing managers for products that compete with NFS use this misconception to claim that NFS is therefore a network bandwidth hog because of all the attribute requests that are sent around. The reality is that the attribute timeouts are checked only whenever a process on the NFS client tries to access the file. If the attribute timeout is 30 seconds and the client has not accessed the file in five hours, then during that five-hour period, there will be no NFS requests to get new attributes. Indeed, there will be no NFS requests at all. For files that are being continuously accessed, with an attribute timeout of 30 seconds, you can expect to get new attribute requests to occur no more often than every 30 seconds. Given that in NFS Version 2, and to an even higher degree in NFS Version 3, attributes are piggy-backed onto the NFS responses, attribute requests would tend to be seen far less often than every 30 seconds. For the most part, attribute requests will be seen most often when the NFS client opens a file. This is to guarantee cache consistency. See Section 7.4.1 for more details.
* * *
acdirmax=n
This option is like actimeo, but it affects the maximum attribute timeout on directories; it defaults to 60 seconds. It can't be higher than 10 hours (36000 seconds).
acdirmin=n
This option is like actimeo, but it affects the minimum attribute timeout on directories; it defaults to 30 seconds. It can't be higher than one hour (3600 seconds).
acregmax=n
This option is like actimeo, but it affects the maximum attribute timeout on regular files; it defaults to 60 seconds. It can't be higher than 10 hours (36000 seconds).
acregmin=n
This option is like actimeo, but it affects the minimum attribute timeout on regular files; it defaults to three seconds. It can't be higher than one hour (3600 seconds).
The nointr, intr, retrans, rsize, wsize, timeo, hard, soft, and ac* options will be discussed in more detail in the Chapter 18, since they are directly responsible for altering clients' performance in periods of peak server loading.
Backgrounding mounts
The mount protocol used by clients is subject to the same RPC timeouts as individual NFS RPC calls. When a client cannot mount an NFS filesystem during the allotted RPC execution time, it retries the RPC operation up to the count specified by the retry mount option. If the bg mount option is used, mount starts another process that continues trying to mount the filesystem in the background, allowing the mount command to consider that request complete and to attempt the next mount operation. If bg is not specified, mount blocks waiting for the remote fileserver to recover, or until the mount retry count has been reached. The default value of 10,000