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
emdevnum <file or directory name>
Example
emdevnum /opt/IBMvast/5.5/manager/mgr55.dat emdevnum /opt/IBMvast/5.5/manager
A typical response might be:
The device number is 21
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.