By default, EMSRV on UNIX permits access to libraries only on certain
known local file systems. This is done to avoid corruptions which can
occur when libraries are stored on networked file systems. If you
intend to locate libraries on a file system that is not recognized by default,
you must specify an -xd option for that file system. If you
do not, your clients will receive a "File resides on an unsupported device"
error when they try to open a library.
emdevnum is a utility which retrieves the major device ID for
the file system of a specified file. The device number reported may
then be used with the emsrv -xd startup option.
EMSRV does not have to be running in order to use
emdevnum.
Syntax
Example
A typical response might be:
WARNING: The -xd option can bypass checking for a remote
file system. If a library is located on a remote file system (or even a
local file system mounted using a remote protocol), the library can become
corrupted. Make sure that devices specific with -xd are
local to the machine running EMSRV and are not from mounted remote file
systems like NFS.
Accessing libraries on remotely-mounted volumes such as those hosted by NFS
may result in library corruptions. This is due to the fact that some
remote file system software cannot guarantee the integrity of a file when
multiple clients are updating it. Although EMSRV uses locks to
serialize access to regions of a library, some locking implementations of NFS,
for example, use UDP, which does not guarantee delivery or the sequence of
transmissions.
On many platforms, NFS file systems return an unusual value (such as 0 or
65535) to emdevnum. However, even if the major device ID
appears to be a reasonable value, check to make sure that device is local to
the machine running EMSRV before specifying it with the -xd
parameter.Determining Local Device Numbers
emdevnum <file or directory name>
emdevnum /opt/IBMvast/5.5/manager/mgr55.dat
emdevnum /opt/IBMvast/5.5/manager
The device number is 21