We had some issues a while back with VSM performance. I did research and experiments with various block sizes for tape data sets. Questions on IBM-MAIN and doc reading yielded some answers--though not necessarily solutions.
-- Tape output is generally faster with larger block sizes. That's easy demonstrate by coding ever larger block sizes. EXCP count and elapsed time will both decrease. -- You can't just increase output block size willy-nilly. A program that uses a traditional DCB is limited to 32K bytes per block. To exceed that value, a program must employ DCBE, which is not hard to use but requires coding changes. -- If you attempt to code >32K block size in JCL for a program with DCB, the value will be ignored and revert to 32K. You might miss that fact because there's no message. Your tape management product (CA-1, RMM, etc.) will show you the actual block size of a file. -- Some IBM utilities are coded with DCBE to enable >32K block size. Others are not. Doc for each utility should indicate the maximum allowable output block size. -- DFSMSdss Storage Administration has this to say: "If the DCB keyword BLKSIZE is specified on the DD statement for tape, it must be in the range of 7,892 through 262,144. If the DCB keyword BLKSIZE is specified on the DD statement for DASD, it must be in the range of 7,892 through 32,760." So DFDSS uses DCBE and can write 256K blocks. In my testing, a job ran quite a bit faster with the maximum block size than with a smaller one. (I did not test DFDSS per se.) But as already indicated, the inhibitor to stellar performance may be on the input side, over which you have little control. . . J.O.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 626-302-7535 Office 323-715-0595 Mobile jo.skip.robin...@sce.com From: Ron Hawkins <ronjhawk...@sbcglobal.net> To: IBM-MAIN@LISTSERV.UA.EDU, Date: 05/13/2014 09:15 AM Subject: Re: Performance for DFDSS with ORACLE Tape Drives VSM5 ( was Change tape block size) Sent by: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> Victor, If I understand problem at the root of your questions, you are trying to speed up DFSMSdss logical dumps, especially for compressed PS-E data sets. >From your questions you are focusing on the tape output rate as the gating factor for the elapsed time of the dump, but have you looked at the time spent processing the input files? I may be having a senior moment, but there are two things that may be affecting the performance of the PS-E data set. (1) I seem to recall that DFSMSdss will process a compressed PS-E data set at block level and not attempt to compress it in order to avoid double compression overhead when COMPRESS is specified, and (2) compressed PS-E data sets do not chain more than one track of at a time. I'll leave it to you to hit the manuals and see if I recall correctly. Considered together this means the input file may well be the choke on the backup performance. It may pay to start some RMF monitor II background sessions at 5 second intervals for the input volumes and output tape addresses and have a look at the make-up of response time on both. Omegamon or similar may also provide a delay analysis that shows where the job is spending its time. An extreme consideration would be to ask if you are using FX8S channels and zHPF? Channel microprocessor usage with Extended format IO was one of the many benefits of zHPF and channel throughput from DASD may be part of your problem. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] > On Behalf Of Lizette Koehler > Sent: Monday, May 12, 2014 7:11 AM > To: IBM-MAIN@LISTSERV.UA.EDU > Subject: Re: [IBM-MAIN] Performance for DFDSS with ORACLE Tape Drives > VSM5 ( was Change tape block size) > > Victor, > > > The blksize is not the only way to tune a process for efficiency. And in some > cases, there is little you can do to affect some applications like DFDSS. > > If you are using the hardware for tape is virtual tape of oracle, vsm5. Then > there may be nothing more you can do. Sometimes the hardware controls > the process. > > I would open an issue with STK and ask them to assist you with this > configuration. There may be a parm or function unique to STK that may help > you. > > I might also open an SR/ETR with IBM DFDSS to see if they have any > suggestions. > > Lizette > > PS I changed the subject to for more visibility > > > > -----Original Message----- > > From: IBM Mainframe Discussion List [mailto:IBM- > m...@listserv.ua.edu] > > On Behalf Of Victor Zhang > > Sent: Sunday, May 11, 2014 11:44 PM > > To: IBM-MAIN@LISTSERV.UA.EDU > > Subject: Re: Change tape block size > > > > Hello, > > First I need thank you who replied to my question. > > I should introduce my problem's background and my concern. > > The tape is virutal tape of oralce, vsm5. > > I am backing up extended format PS dataset to VSM5 using ADRDSSU. > > I tested using dss to backup, no matter what block size I specified in > > JCL, ADRDSSU will report same number of blocks in message IEC205I. > > And the backup speed will also be same no matter what block size I > > specified in JCL. > > Here is my testing result: > > st_TIME end_TIME backup source data type VOLSER > VTV > > size(mb) VTV size(comp)(mb) tape block size(KB) Total block > count > > reported by DSS backup speed(MB/S) > > 11:31:41 11:33:12 Extended format compressed AB3968 > > 1854.15 647.77 128 33879 20.38 > > 11:33:12 11:34:42 Extended format compressed AB3974 > > 1854.15 647.77 64 33879 20.60 > > 11:34:42 11:36:17 Extended format compressed AB3976 > > 1854.15 647.77 256 33879 19.52 > > > > But this is not true for BASIC PS dataset, for basic PS dataset, I > > did a similar > > testing: > > st_TIME end_TIME backup source data type VOLSER > VTV > > size(mb) VTV size(comp)(mb) tape block size(KB) Total block > count > > reported by DSS backup speed(MB/S) > > 13:08:07 13:11:37 Basic PS AB4075 6273.86 360.15 > > 128 49117 29.88 > > 13:11:37 13:16:00 Basic PS AB4078 6274.57 367.9 > > 64 98426 23.86 > > 13:16:00 13:19:04 Basic PS AB4082 6273.51 355.52 > > 256 24528 34.10 > > > > Please note the total block count reported by DSS is different when > > specifying different tape block size. > > > > My goal was: > > To improve backup performance for extended format PS dataset(DB2 > image > > copy on dasd)using ADRDSSU,I am trying to use 256KB to improve > > performace,but I can't. > > Do you have any ideas? > > > > > > Regards > > Victor ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
