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Move file from Tape to DASD - Performance improve?

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Move file from Tape to DASD - performance improve

Yes - CPU, IO and Elapsed time

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Yes - only Elapsed time

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#1: Move file from Tape to DASD - Performance improve? Author: vak255,

Posted: Tue Jun 03, 2014 12:52 pm
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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.

#2: Re: Move file from Tape to DASD - Performance improve? Author: kolusu, Location: San Jose

Posted: Tue Jun 03, 2014 1:22 pm
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vak255 wrote:

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

A poll is quite unnecessary, secondly who ever believed in the notion that moving tape to DASD will improve I/O is so wrong. With Tapes you can have a BLOCKSIZE of 256k which would beat the Track size blocking of DASD files on any given day. DASD I/O depends on Number of Channel Programs and the buffers.

vak255 wrote:

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. [b]There should be no CPU or IO savings. Experts please advise, If I am wrong.

Read above

#3: Author: Terry_Heinze, Location: Richfield, MN, USA

Posted: Tue Jun 03, 2014 1:26 pm
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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".

#4: Author: vak255,

Posted: Wed Jun 04, 2014 9:53 am
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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.

#5: Author: vak255,

Posted: Wed Jun 04, 2014 10:19 am
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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?

#6: Author: William Collins,

Posted: Wed Jun 04, 2014 10:53 am
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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.

#7: Author: kolusu, Location: San Jose

Posted: Wed Jun 04, 2014 11:07 am
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vak255 wrote:

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

Yes. If you code DISP=SHR on all the jobs. For tapes it is just 1 job at a time.

vak255 wrote:

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

I have no idea as to where you got the information that we load each record into main memory be it tapes or DASD. You might want to read this article about DASD I/O Programming which will give you a better understanding of how I/O is performed.

#8: Author: vak255,

Posted: Wed Jun 04, 2014 11:52 am
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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.

#9: Author: vak255,

Posted: Tue Jun 10, 2014 10:33 am
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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.

#10: Author: vak255,

Posted: Tue Jun 10, 2014 10:34 am
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**Update --- I used the same records for both the copy cases.

#11: Author: Terry_Heinze, Location: Richfield, MN, USA

Posted: Tue Jun 10, 2014 12:30 pm
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The time it took to mount the tape should be indicated by the Job's JESMSGLG.

#12: Author: vak255,

Posted: Tue Jun 10, 2014 12:37 pm
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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?

#13: Author: kolusu, Location: San Jose

Posted: Tue Jun 10, 2014 3:52 pm
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vak255 wrote:

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,

You need to realize that people do NOT have access to your sysout or have an idea about the files that are being copied. So you need to provide as much details as you can.

1. What is the LRECL/RECFM/BLKSIZE of the input file being copied?
2. Are they run at the same time? or is the load on the system the same?
3. What is the elapsed time on the tape job that consumed more CPU?
4. What utility did you use to copy the Tape and DASD Files?

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