Hi,
In a series of recent posts entitled "Re: z/OS 1.9 Features summary" there
was a debate about the default number of buffers with views offered as to
whether it is 2 or 5 with claims that the documentation states 2.
Well there is scope for differing opinions on the default BUFNO as it varies
for different file types. Below is an extract from the z/OS 1.6 Dataset
Macros manual (QSAM section only), and even here the variance is plain to
see.
<EXTRACT>
BUFNO=absexp (maximum value is 255)
specifies the number of buffers that are acquired automatically during OPEN.
If chained scheduling is specified, the value of BUFNO also determines the
maximum number of channel program segments that can be chained and must
be specified as more than one. If BUFNO is omitted and the buffers are
acquired automatically, the system acquires:
- 1 for a PDSE member
- 1 for an extended format data set in compressed format
- 1 for a USS file
- (2 * number of stripes * number of blocks per track) for an extended
format data set if it is not in the compressed format
- 2 if the block size is greater than or equal to 32768
- 3 for an IBM 2540 card reader or card punch
- 5 for other types of devices or data sets
</EXTRACT>
My guess is that many traditional disk data sets fall into the latter
category of 5 buffers however.
Kind regards - Terry
Terry Sambrooks
Director
KMS-IT Limited
228 Abbeydale Road South
Dore, Sheffield, S17 3LA, UK
Tel: +44 (0)114 262 0933
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