Whats mounting and demounting in tapes

sudhanaveenkumar · New User Joined: 29 Apr 2010 Posts: 28 Location: chennai

Hi..

can any one of you tell me whats this mounting and demounting for tapes.

Why is this required.

In case of tapes.. while defining new tape we use unit=(tape,defer)... why is this defer user?///

Thanks
naveen

sudhanaveenkumar · New User Joined: 29 Apr 2010 Posts: 28 Location: chennai

Hi all...

in case of non vsam files, DCB is stored in VTOC.For VSAM-- ITS STORED IN CATALOG.Whats the advantage of storing DCB in catalog?

Thanks
Naveen

expat · Posted: Tue Jul 27, 2010 12:55 pm

One can only assume that these are interview or homework questions.
Moved to this forum.

Robert Sample · Posted: Tue Jul 27, 2010 4:07 pm

3480 / 3490 / 3590 tapes are physical media about the size of an 8-track tape cartridge (if you ever saw one of those). Tapes are cheap while tape drives to access the data on tapes are much more expensive. Tape libraries therefore allow access to many, many more tapes than tape drives (most libraries will hold tens of thousands of tapes while having some 4 to 32 tape drives). Mounting a tape is the process of finding it and loading it into a tape drive so the data can be read (or written). Demounting (or unmounting to use the more common term) is the process of rewinding the tape and ejecting it from the tape drive to it can be returned to its storage spot. JES will generally mount tapes when a job starts up; defer in the JCL causes the tape mount to be done when the tape is needed, not at job start.

The first problem with your second post is that VSAM does not store DCB data in the catalog. A VSAM file does not have a DCB so there is no data to be stored anywhere. The second problem is where did you hear that this data is stored in the catalog ? All the catalog has is the data set name, volume the data set resides on, and the type of media the volume is. File details are stored in the VTOC or tape header not the catalog.

Gousiya Mulla · New User Joined: 02 Jun 2008 Posts: 87 Location: Bangalore

I heard several times from the support guys that 'Tapes need to mount' (physical tapes) . In this case is this a physical movement or through running a job.

Any additional information on this will be very useful !!

Robert Sample · Posted: Tue Jul 27, 2010 4:40 pm

It typically is done through a job which requests a particular tape (or no particular tape for an output, or scratch, volume). The mount is physical movement of the tape from wherever it is located to the tape drive and insertion of the tape into the tape drive so it can be read or written.

sudhanaveenkumar · New User Joined: 29 Apr 2010 Posts: 28 Location: chennai

Hi Robert,

Many Thanks for your prompt reply.

I am clarified for the first question.

Regarding VSAM question: I have read Murah Jcl book.It says VSAM is catalog driven and all the details of file are stored in catalog(Including DCB).

As per your stmt above(i.e . File details are stored in the VTOC or tape header not the catalog), if VSAM file DCB details are stored in VTOC,then why cant we access an uncatalogged VSAM file and why every vsam file has to be catalogged?

Thanks
Naveen[/b]

Robert Sample · Posted: Tue Jul 27, 2010 6:54 pm

Gousiya Mulla · New User Joined: 02 Jun 2008 Posts: 87 Location: Bangalore

dick scherrer · Posted: Wed Jul 28, 2010 9:29 am

Hello,

Virtual Tape (or Vtape) creates logical tape volumes on dasd. Virtual Tape Drives are defined to process these virtual tapes (if you look at the jes log of 2 jobs that use "real" tapes and virtual tapes, you will notice that the tape drive numbers (UCB) for the virtual tapes and the real tapes are not in the same series.. These "tapes" are still managed by the tape management system (i.e. CA-1). They are just created in different tape pools within the tape management system.

The normal "mount" messages still appear on the console (unless they have been inhibited).

Virtual tapes are usually copied onto 3590 (FAT) tapes which may be taken offsite for storage.

And no, the virtual tapes themselves are not physically taken offsite for storage.

Gousiya Mulla · New User Joined: 02 Jun 2008 Posts: 87 Location: Bangalore

Thanks Dick and Robert !

sudhanaveenkumar · New User Joined: 29 Apr 2010 Posts: 28 Location: chennai

Many Thanks Robert and Dick.

I am clarified for the second question as well now.

Thanks
Naveen

Bill Dennis · Posted: Wed Jul 28, 2010 8:16 pm

Some virtual tape implementations archive virtual volumes to physical tapes to free disk space. A recall of this vitrual volume will require a physical mount on the back end (robotics?) and lead to a delay of a few minutes. The backend activity is hidden from your Job.

Dadi Krishna Teja · New User Joined: 16 May 2019 Posts: 5 Location: India

Can someone give me JCL to copy such mounted tapes to a Mainframe file.

Rohit Umarjikar · Posted: Thu May 16, 2019 11:24 pm