HP CIFS Server 3.0f Administrator's Guide verison A.02.03

Special Issues When Using CFSM
This section describes special issues when using CFSM.
NFS delayed write errors with CFSM
Due to the way NFS is designed and the caching it does for improved performance, NFS clients may get
"delayed write errors" in various situations. This means that a write to a file on an NFS mounted file
system may appear to succeed, when in reality it has failed. An error code returned on a later write operation
or when the file is closed is used to notify applications that an earlier write has failed. Poorly written
applications, which don't check for errors when a file is closed for example, may experience data loss
because the failed write went unnoticed. This can happen even when CFSM is not being used.
Using CFSM on a file system that is shared by NFS introduces another scenario where NFS clients might
get delayed write errors. If this increased chance of delayed write errors on NFS clients is unacceptable,
the use of the "noac" (no attribute caching) option when mounting the NFS file system eliminates the possibility
of delayed write errors. However, the use of the "noac" option will significantly reduce the performance of
any NFS file system that uses it, because NFS caching is turned off.
Memory Mapped Files with CFSM
In order to properly enforce the CIFS file locks, CFSM can't allow files with CIFS file locks to be memory
mapped. What this means in practice is that any attempt to memory map a file with CIFS file locks will fail,
and also that any attempt by a CIFS client to acquire a file lock on a memory mapped file will fail.
This should not be an issue because CIFS clients and NFS clients can't memory map files, only local processes
can. So files shared between CIFS clients and NFS clients can't be affected by this.
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