jb.1234abcd at gmail.com
Thu Sep 30 02:25:05 UTC 2010
JB <jb.1234abcd <at> gmail.com> writes:
There are other things to consider.
$ man 5 exports
$ man 5 nfs
Valid options for either the nfs or nfs4 file system type
wsize=n The maximum number of bytes per network WRITE request
that the NFS client can send when writing data to a file
on an NFS server. ...
ac / noac Selects whether the client may cache file attributes.
The noac option is a mixture of a generic option, sync, and
an NFS-specific option actimeo=0. So it causes a significant performance
But do not confuse file attributes caching with data caching.
The sync mount option
The NFS client treats the sync mount option differently than some other
file systems (refer to mount(8) for a description of the generic sync
and async mount options). If neither sync nor async is specified (or
if the async option is specified), the NFS client delays sending appli-
cation writes to the server until any of these events occur:
Memory pressure forces reclamation of system memory resources.
An application flushes file data explicitly with sync(2),
msync(2), or fsync(3).
An application closes a file with close(2).
The file is locked/unlocked via fcntl(2).
In other words, under normal circumstances, data written by an applica-
tion may not immediately appear on the server that hosts the file.
If the sync option is specified on a mount point, any system call that
writes data to files on that mount point causes that data to be flushed
to the server before the system call returns control to user space.
This provides greater data cache coherence among clients, but at a sig-
nificant performance cost.
Applications can use the O_SYNC open flag to force application writes
to individual files to go to the server immediately without the use of
the sync mount option.
NFS version 4 caching features
A file delegation ...
... Once a file has been delegated to a client, the client can cache
that file’s data and metadata aggressively without contacting the
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