Ed Jaffe wrote:
<snip>
I never liked defining secondary of zero. I realize it's IBM's
recommendation, but it all but ensures a compress will be performed when
the library fills up. I've had systems crash either during or after such
a compress -- sometimes with disastrous consequences!
<snip>
Whether it's "IBM's" recommendation depends on who you talk to (smile).
I believe Peter and I have disagreed about this for about 25 years.
There are two possible problems when using secondary extents for link
list data saets, exceeding the link list extent limit the topic of this
thread, everyone's favorite ABEND106-F RC40. If your link list is not
especially long, hitting the 255 limit will probably not happen; you can
count extents before IPL after putting on PTFs and if necessary compress
or reallocate. In the meantime, you will have many fewer x37 abends
while putting on PTFs. This should be an informed choice, in my view,
rather than a blanket recommendation. But see below.*
If you don't update running systems, the second problem will never occur.
Likewise, whether it's IBM's recommendation to never update a copy of
system software that is in use depends on who you talk to and whether
DYNACT is specified for a particular PTF. Here there be tygers, and my
recommendation is never to do that unless you clearly and thoroughly
scope out the probable result first and are prepared to IPL if you miss
something (which is easy to do) and the change goes pear-shaped.
*I expect most people to move to thin provisioned volumes over time
because the business case is compelling. On TP volumes, there is no
reason not to use very large primary extents, which can obviate any
advantage to secondary space allocation for system software volumes.
"Just let the disk controller manage the actual real estate" is my (new)
recommendation for system software volumes.
--
John Eells
IBM Poughkeepsie
[email protected]
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