NOAC
Use the noac mount option to achieve attribute cache coherence
among multiple clients. Almost every file system operation checks file
attribute information. The client keeps this information cached for a
period of time to reduce network and server load. When noac is in
effect,a client’s file attribute cache is disabled,so each operation
that needs to check a file’s attributes is forced to go back to the
server. This permits a client to see changes to a file very quickly,
at the cost of many extra network operations.

lookupcache=none
If the client ignores its cache and validates every
application lookup request with the server,that client can
immediately detect when a new directory entry has been either created
or removed by another client. You can specify this behavior using
lookupcache=none. The extra NFS requests needed if the client does not
cache directory entries can exact a performance penalty. Disabling
lookup caching should result in less of a performance penalty than
using noac,and has no effect on how the NFS client caches the
attributes of files.

actimeo=n
Using actimeo sets all of acregmin,acregmax,acdirmin,and acdirmax to the same value.

• acregmin=n,The minimum time (in seconds) that the NFS client caches attributes of a regular file before it requests fresh
  attribute information from a server. If this option is not
  specified,the NFS client uses a 3-second minimum.
• acregmax=n,The maximum time (in seconds) that the NFS client caches attributes of a regular file before it requests fresh
  attribute information from a server. If this option is not
  specified,the NFS client uses a 60-second maximum.
• acdirmin=n,The minimum time (in seconds) that the NFS client caches attributes of a directory before it requests fresh attribute
  information from a server. If this option is not specified,the NFS
  client uses a 30-second minimum.
• acdirmax=n,The maximum time (in seconds) that the NFS client caches attributes of a directory before it requests fresh attribute
  information from a server. If this option is not specified,the NFS
  client uses a 60-second maximum.

取自NFS man page.

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