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Status Future consideration
Workspace z/OS
Categories DFSMS Access Methods Non-Vsam
Created by Guest
Created on Apr 21, 2021

RELATED IDEAS

BUFNO calculation for Extended format sequential datasets

BUFNO are calculated according to the following formula:

n—Extended format but not compressed format and not LBI (n = 2 × blocks per track × number of stripes)
1—Compressed format data set, PDSE, SYSIN, SYSOUT, SUBSYS, UNIX files
2—Block size > =32,760
3—2540 Card Reader or Punch
5—All others

We recognized that without BUFNO= specification the runtime for Basic/Large format datasets is about 40% smaller than for Extended format datasets. Media Manager for Extended format datasets writes out per CI. The number can't be influenced by MM itself, but the BUFNO calculation could.

Adding BUFNO to Extended format datasets indirectly has an influence to the I/O speed.

So, the default calculation of BUFNO for Extended format datasets should be re-thought to get at least the performance as it is for Basic/Large format datasets.

Idea priority Medium
  • Guest
    Reply
    |     Apr 22, 2021

    Is this a request for System Managed Buffering for non-VSAM data sets?

  • Guest
    Reply
    |     Apr 22, 2021

    Case: TS005380303 / Severity: 2 / Haftpflicht-Unterstützungs-kasse / Question regarding Sequential Dataset performance

    This is Tom Wai from IBM SMS/BAM support team for this case. I recreated the issue in my sandbox by using IEBCOPY (COPYGROUP) on a PDSE loadlib.
    I ran GTF I/O trace on the three formats of an output data set (ie Basic / Large / Extended) with the following findings which likely explain why the run times are varied. Mainly, it is the different numbers of data-block being written out to the data set causing the difference. The use of BUFNO specification with a bigger value improves the performance significantly, especially for an extended format data set.

    Without BUFNO specification (ie default):
    ----------------------------------------------
    BASIC / LARGE format - 5 IDAWs of x'11C' bytes of data each.
    EXTENDED format - 1 MIDAW of x'1014' bytes of data followed by x'6FEC' bytes of low values and an x'20' bytes suffix.

    With a specification of BUFNO 192:
    ----------------------------------------
    BASIC / LARGE format - 10 IDAWs of x'11C' bytes of data each.
    EXTENDED format - 5 MIDAWs of x'1014' bytes of data followed by x'6FEC' bytes of low values and an x'20' bytes suffix for each set.


    CCW Dev# Number
    --------------------------------------------
    SSCH/IO.... 0C154 14302 (Basic)
    SSCH/IO.... 0C165 6619 (Basic with bufno)

    SSCH/IO.... 09468 14320 (Large)
    SSCH/IO.... 0C14F 6606 (Large with bufno)

    SSCH/IO.... 09468 18107 (Extend)
    SSCH/IO.... 0C166 3696 (Extend with bufno)

    Brgds. - Tom Wai

  • Guest
    Reply
    |     Apr 21, 2021

    Due to processing by IBM, this request was reassigned to have the following updated attributes:
    Brand - Servers and Systems Software
    Product family - z Systems Software
    Product - z/OS
    Component - DFSMS Access Methods Non-Vsam
    Operating system - IBM z/OS
    Source - None

    For recording keeping, the previous attributes were:
    Brand - Servers and Systems Software
    Product family - z Systems Software
    Product - z/OS
    Component - DFSMS Media Manager
    Operating system - IBM z/OS
    Source - None

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