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vak255 · Intermediate Joined: 10 Sep 2004 Posts: 384 Topics: 79

I have been told that moving a large data file from tape to DASD will improve I-Os, CPU, Elapsed time.

I believe moving a data file from tape to DASD will only save the elapsed time since the job don't have to wait for the tape to be mounted.
There should be no CPU or IO savings.
Experts please advise, If I am wrong.

Thanks for your time.

kolusu

Terry_Heinze · Posted: Tue Jun 03, 2014 1:26 pm Post subject:

Since many sites use robotic tape mounting (or whatever it's called), tape mount time is oftentimes minimal. I've also read that tape is just as fast as disk with the newer technololgy. I think you need more choices in your survey. At least one more: "No - Very little noticable difference".
_________________
....Terry

vak255 · Intermediate Joined: 10 Sep 2004 Posts: 384 Topics: 79

Thanks Kolusu & Terry.

Terry - I added 'No' to the survey but I believe I did not hit the 'save' to add that option. Sorry for that.

vak255 · Intermediate Joined: 10 Sep 2004 Posts: 384 Topics: 79

question:
Is the below are true. Its does not make sense to me. please excuse me for posting this but I like to know your comments.

1. files can be concurrently accessed by many programs if the file is on DASD rather than tape?

2.Files can be accessed and opened instantaneously, No need to load into main memory for each record as it is happening in Tape?

William Collins · Supermod Joined: 03 Jun 2012 Posts: 437 Topics: 0

If you need a file to be open in more than one place at the same time, then that file can't be on tape.

I'm not sure what you mean by the second sentence in your number 2.

There are always specifics about the data which dictate what media are candidates. If the data is for use in CICS, it will not be on tape. If you want the most rapid backup, and your hardware and software support it, you would use tape with Large Blocking Factor.

Other than that, you need some work on how physical and logical records on recorded media become physical and logical records in memory, and logical (mostly) records in a program.

A lot of what people just "say" is not worth the air expended in saying it.

kolusu · Posted: Wed Jun 04, 2014 11:07 am Post subject:

vak255 · Intermediate Joined: 10 Sep 2004 Posts: 384 Topics: 79

Thanks for the details, Kolusu.

I got these details from one of the team member's proposal to change Tape files to DASD. These were the reasons given.

vak255 · Intermediate Joined: 10 Sep 2004 Posts: 384 Topics: 79

I checked the CPU time from Copying records from Tape to DASD and then DASD to DASD. I see that CPU time is little high for copying records from Tape to DASD compared to DASD to DASD.

Is this because of the Read speeds of Tape or time to mount the tape ?

Thanks for your time.

vak255 · Intermediate Joined: 10 Sep 2004 Posts: 384 Topics: 79

**Update --- I used the same records for both the copy cases.

Terry_Heinze · Posted: Tue Jun 10, 2014 12:30 pm Post subject:

The time it took to mount the tape should be indicated by the Job's JESMSGLG.
_________________
....Terry

vak255 · Intermediate Joined: 10 Sep 2004 Posts: 384 Topics: 79

Thanks Terry, I will check on it.
The time took to mount the tape should be the elapsed time.

Do you think there will be CPU expense for mounting the tape?

kolusu · Posted: Tue Jun 10, 2014 3:52 pm Post subject: