HP CIFS Server Administrator Guide Version A.02.04.04 (5070-6710, October 2011)

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.
CFSM Tracing
The CIFS File System Module provides diagnostic functionality to trace the CFSM activities by
sending trace messages to a log file. All of CFSM tracing are controlled through the cfsmutil
command.
NOTE: If the CIFS File System Module is not used by any file systems then it will not be loaded,
cfsmutil will not function, except for the help (-h) option.
cfsmutil Command
Use the cfsmutil command to control and retrieve various CIFS File System Module tracing
parameters.
Syntax
cfsmutil [option]
where option can be any of the following:
-i Displays the current parameters and trace state. The parameters
displayed are:
CFSM Tracing on/off
CFSM Tracing level
CFSM Tracing file name
CFSM Tracing file maximum size
-s Enables the CFSM tracing.
Special Issues When Using CFSM 141