View previous topic :: View next topic
|
Author |
Message |
gylbharat
Active Member
Joined: 31 Jul 2009 Posts: 565 Location: Bangalore
|
|
|
|
Hi,
I observed a strange thing. I was running two parallel jobs - Unload from IMAGE COPY for two different tables.
The image copy of both the tables reside on the same tape volume.
When both the jobs were running simultaneously - I saw one job was actually waiting for the Volume to be available.
Both the jobs were using disposition as SHR. but still not sure why the job was waiting for the volume. |
|
Back to top |
|
|
dick scherrer
Moderator Emeritus
Joined: 23 Nov 2006 Posts: 19244 Location: Inside the Matrix
|
|
|
|
Hello,
Why in the world would you use SHR for a tape? It makes no sense (imagine the poor tape drive trying to spin back and forth to take turns) to consider sharing tape. There are some reasons to use shr for a tape, but they have nothing to do with your request.
Two processes cannot allocate/use the same tape. |
|
Back to top |
|
|
vasanthz
Global Moderator
Joined: 28 Aug 2007 Posts: 1742 Location: Tirupur, India
|
|
|
|
Hello D,
I am aware it is normal that when a job uses a tape, the other jobs which require that tape would wait until the tape is available.
Just curious, Is the same true for VTS tapes as well?
I have heard that one of our clients use VTS tapes for some datasets, but I have not used them so far to test it out. |
|
Back to top |
|
|
dick scherrer
Moderator Emeritus
Joined: 23 Nov 2006 Posts: 19244 Location: Inside the Matrix
|
|
|
|
Hi Vasanth,
Quote: |
Just curious, Is the same true for VTS tapes as well? |
As far as i know. . .
I've been thru several v-tape migrations, but these systems would not promote a job to producton with SHR specified for a tape unit so i never tried.
When data is migrated to v-tape, there need be no program changes and the only jcl change i remember is to use the new generic/esoteric (several use UNIT=VTAPE). |
|
Back to top |
|
|
gylbharat
Active Member
Joined: 31 Jul 2009 Posts: 565 Location: Bangalore
|
|
|
|
Thanks Dick ... I was not able to figure out why it was actually happening... Thanks....
Can you also please elaborate on - when to use SHR for TAPE ? |
|
Back to top |
|
|
prino
Senior Member
Joined: 07 Feb 2009 Posts: 1306 Location: Vilnius, Lithuania
|
|
|
|
gylbharat wrote: |
Thanks Dick ... I was not able to figure out why it was actually happening... |
And you call yourself a "Software Engineer"?
How the fluffing hell did you ever get your current job, when you cannot even figure out that, as DS wrote, you cannot read a tape at two places at the same time?
Please change the title in your profile to "Mainframe novice", your current title is about 42 levels over your qualifications. |
|
Back to top |
|
|
Robert Sample
Global Moderator
Joined: 06 Jun 2008 Posts: 8696 Location: Dubuque, Iowa, USA
|
|
|
|
You can use DISP=SHR for a tape data set any time you want. The tape will not be shared, of course, since the tape drive (real OR virtual) can only be at one spot on the tape at a time.
From the JCL Language Reference manual, section 12.19.2.1:
Quote: |
If you specify DISP=SHR for an output tape data set and (1) the data set is not protected by RACF or a password or (2) the data set has no expiration date, the system does not verify the data set name in the header label. |
So there are reasons other than data set sharing to use DISP=SHR.
And Appendix 1.2.2.3 of the JCL User's Guide help clarify the usage:
Quote: |
Indicates that you are willing to share the data set
with other jobs. This subparameter alone, however,
does not guarantee that sharing will take place. See
z/OS DFSMS Using Data Sets for a full description of
data-set sharing. |
|
|
Back to top |
|
|
gylbharat
Active Member
Joined: 31 Jul 2009 Posts: 565 Location: Bangalore
|
|
|
|
prino wrote: |
gylbharat wrote: |
Thanks Dick ... I was not able to figure out why it was actually happening... |
And you call yourself a "Software Engineer"?
How the fluffing hell did you ever get your current job, when you cannot even figure out that, as DS wrote, you cannot read a tape at two places at the same time?
Please change the title in your profile to "Mainframe novice", your current title is about 42 levels over your qualifications. |
Being a software engineer doesn't mean one know every thing in software industry ... This is an open forum... and I am here to learn... I know tapes are sequential data sets... But some how not able to figure out the reason in this case... |
|
Back to top |
|
|
gylbharat
Active Member
Joined: 31 Jul 2009 Posts: 565 Location: Bangalore
|
|
|
|
Thanks Robert... This is useful... |
|
Back to top |
|
|
gcicchet
Senior Member
Joined: 28 Jul 2006 Posts: 1702 Location: Australia
|
|
|
|
Hi,
it's possible the dataset may have resided on DASD and now its on tape,
maybe the reason for the DISP=SHR.
VTS datasets are treated the same as tape datasets.
Gerry |
|
Back to top |
|
|
|