At CASPUR, we have several automated services that make use of tape drives. These drives are shared over the fibre channel SAN. And often the same physical tape drive is called differently on different machines, in function of the system architecture and the way it was configured on each host. For instance, on some Linux machine a drive may be accessed as "/dev/st0", and at the same time on another AIX machine this very drive will be called /dev/rmt3, and on yet another Solaris host it will be named "/dev/rmt/2" etc.

On the top of this, same drive (or tape) may be claimed by several processes at the same time, and this has to be handled somehow. Our structure is even more complex, as the same magnetic tape may be mounted on the same host but on the different tape drives. And we have to handle several different tape types (LTO, STK9840, DLT, AIT).

To address the management issues that arise in this distributed environment, we have introduced the CASPUR Tape Dispatcher. This application 1) is doing a minimal bookkeeping of tape resources (both drives and magnetic tapes); 2) is handling tape mount requests, i.e. mounts and unmounts tapes, and 3) takes care of the resource "locking", or simply ensures that only one process at a time may use one specific resource, such as a tape drive or some magnetic tape.

We believe that our solution may be of interest also for other sites. It may be used to handle multiple mount requests on one or many tape mounters via the site-specific mount commands. And it is especially useful in cases when several independent and asynchronous tasks that run on the same or different hosts may simultaneously require the same tape resource.