HP CIFS Server 3.0k Administrator's Guide version A.02.04

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.
166 CIFS File System Module (CFSM) Support