On 17 Mar 2006 10:22:46 -0800,
[EMAIL PROTECTED] (Jerry Whitteridge) wrote:
>Then I'm confused. ETR = External Time Reference = Sysplex Timer
>( If I want to see the status of my sysplex timer I issue the command D
>ETR)
>What leads you to write ETR != Sysplex Timer ? (I'm curious -- with the
>exception of a parallel sysplex running on a single footprint (which I
>agreed I forgot) I know of no other way to run a parallel sysplex(with
>or without VM))
I'll trust the experts on this list to correct me if I'm wrong, but here's
a diagram that illustrates the relationship between the systems in the
plex, the sysplex timer and the ETR (as I understand the architecture):
(The diagram is best viewed with a fixed-pitch font.)
+----------+ +----------+ +----------+
| | | | | |
| zOS A | | zOS B | | zOS C |
| | | | | |
+----------+ +----------+ +----------+
| | |
| | |
+---------------+---------------+
|
|
+---------+
| Sysplex |
| Timer |
+---------+
|
|
+---------+
| ETR |
+---------+
|
|
+---------+
| NIST |
| GPS |
| etc |
+---------+
The z/OS systems might be LPARs on the same physical box, or LPARs on
completely separate boxes; I believe the architecture is the same in
either case.
The sysplex timer is the device that makes sure the TOD clocks in all the
systems in the plex are in synch. However, that synchronization has no
direct correlation with the outside world. If the plex has no ETR, then
over time the TOD clocks may drift and no longer accurately match
real-world time of day. However, the sysplex timer insures that ALL of the
TOD clocks in the plex will be off BY THE SAME AMOUNT.
If you then acquire an ETR, it serves as an interface between your
external time source and the sysplex timer. Somehow, through magic I don't
know anything about, the ETR will feed correct time-of-day information to
the sysplex timer. The sysplex timer, in turn, will feed corrections to
the systems in the plex so that the TOD clocks are not only in sych, but
also match real-world time.
As Dave Kopischke mentioned in a previous post, it sounds like current
zServer systems can use "something called a CLO card in the timer" to
maintain synchronization with an external time source. Sounds like the CLO
card performs the functions of the ETR; I'll have to defer to Dave on
this, since I don't have any knowledge of CLO cards.
Eric
--
Eric Chevalier E-mail: [EMAIL PROTECTED]
Web: www.tulsagrammer.com
Is that call really worth your child's life? HANG UP AND DRIVE!
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