On 2/18/2004 5:26 PM Jim Sibley wrote:
John wrote:
I wouldn't say that VSAM is standardized at 4K
blocks.
In general:
A Control Interval can be any size from 512 to 8192
bytes in increments
of 512 bytes, and from 8 KB to 32 KB in increments of
2 KB.
The underlying physical record size is chosen by
VSAM, and depends on device geometry. The physical
record size is equal to or less than the CI size, and
divides into CI size with no remainder.
For quite some time, VSAM has been using the media
manager as its device driver. The standard block on
disk is 4K and all I/O's are 4K, even though the CI
may change in size. Unless you have something older
than a 3380 or an very old MVS, a track dump would
show that the actual blocks on disk are 4K.
<sigh> Media Manager? Sounds like there's a thing or two about z/OS I
don't know. I've not seen reference to it in manuals (DFSMS: Using Data
Sets, for example). Does VSAM know that all I/O's are 4K, or is the
Media Manager a whole 'nother layer?
Oh, nevermind... no need to educate me about this, especially on this
fine list. I don't currently do mainframes for a living, and z/Linux
really has nothing to do with z/OS's Media Manager (as far as I know).
Also, if you looked at PDSE data sets and QSAM
extended data sets, the blocksize on disk will be 4K!
MVS has for some time been moving towards a fixed 4K
block. The problem is the data in the field has to
catch up.
=====
Jim Sibley
RHCT, Implementor of Linux on zSeries
--
jcf
