On 03/02/2012 09:41 PM, George Kozakos wrote:
On 02/03/2012 08:36 PM, Joel C. Ewing wrote:
In absence of sysplex timer or the like, the processor TOD clock is set
only at POR and is set based on the HMC clock, which may in turn sync
once a day with the SE clock.
The SE is sync'd to the CEC TOD and the HMC is sync'd to the SE.
The SE is sync'd to the CEC TOD every 24 hours, 4 hours or 1 hour depending
on MCL level. The current best practice is to keep the CEC TOD accurate via
an external time source which in turn keeps the SE and HMC accurate. This
requires STP or sysplex timers.
George Kozakos
z/OS Software Service, Level 2 Supervisor
The CEC sync on more recent machines had slipped my memory. On those
systems, to see a significant jump in TOD time at POR, one would have to
manually set the SE time, do a poor job of it, and do it close enough to
POR so SE time doesn't get reset by the CEC TOD, yet far enough away
(several minutes?) to be sure it propagated to HMC.
Particularly now that STP is just a matter of code rather than hardware,
it makes less and less sense (from the customer's viewpoint of course)
for this to be a chargeable feature, which was still the case when I
last checked. As long as it is a chargeable feature it is hard to
cost-justify unless you are running a multi-system sysplex environment
that requires it or you have some unusual requirement that really
demands your TOD clock be that accurate. That it is the "best practice"
and the only sure way for keeping the TOD clock accurate makes it nice
to have for a number of reasons; but if management asks if it is a "must
have" additional expense or a feature you can live without, in many
cases the latter response must be given.
--
Joel C. Ewing, Bentonville, AR [email protected]
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