topic Re: MC/SG, NTP and "date -a" in Operating System - HP-UX

MC/SG, NTP and "date -a"

Abhik Sarkar_1 — Thu, 29 Apr 2004 03:19:55 GMT

We have a couple of L2000 servers in a SG cluster.
* The servers run Oracle (containing mostly static configuration data)
* They also run mission critical telecoms application.
* The servers have NTP configured, with each machine setup as the other's peer.
* The machines are load-sharing and not active-standby.

The time on the machines happens to about 12 minutes ahead of the actual time. I want to know if there is any way in which I can change the time backwards safely without bringing down both systems together (and hence causing a service outage).

I tried issuing a "date -a" on one of the machines expecting the other to sync, but it didn't seem to have any effect. I wonder if it has anything to do with the setting up of the machine as NTP peers.

Any help will be greatly appeciated.

Many thanks,
Abhik.

Re: MC/SG, NTP and "date -a"

Bernhard Mueller — Thu, 29 Apr 2004 03:40:01 GMT

Abhik,

run the same "date -a -60" command on all your NTP peers at about the same time (e.g.via cron or at)

Then verify that all are only 11 minutes ahead. Then either use a larger number or repeat the cronjob a couple of times.

Regards,
Bernhard

Re: MC/SG, NTP and "date -a"

V.Tamilvanan — Thu, 29 Apr 2004 03:41:58 GMT

Hi,

1.Disable the ntp daemon on both the server.
2. Issue date -a command on both the servers.
3. Check after a day or two whether both the servers time are sync with the actual time. then enable the ntp daemon.

Re: MC/SG, NTP and "date -a"

Abhik Sarkar_1 — Thu, 29 Apr 2004 03:50:35 GMT

Hi,

Thanks for your replies.

Tamil, I have thought of your idea before, but I wonder if SG has somekind of dependency on NTP. Is it OK to disable NTP on a SG cluster?

Thanks,
Abhik.

Re: MC/SG, NTP and "date -a"

V.Tamilvanan — Thu, 29 Apr 2004 03:53:07 GMT

Hi Abhik,

It is OK. No problem.

Re: MC/SG, NTP and "date -a"

Robert-Jan Goossens — Thu, 29 Apr 2004 03:57:04 GMT

Hi Abhik,

No there is no problem disableling ntp on a service guard cluster for a period to sync the time ( using date -a As Bernard and Tamil suggested).

HTH,
Robert-Jan

Re: MC/SG, NTP and "date -a"

Abhik Sarkar_1 — Thu, 29 Apr 2004 05:04:01 GMT

Thanks everyone.

I will try the following on the live servers and let you know the result:

* Disable NTP on both nodes.
* Add the cron jobs on both nodes
* Check after a few hours if the time has synced with the actual time.
* Re-start NTP on both nodes.

Best regards,
Abhik.

Re: MC/SG, NTP and "date -a"

Tim Howell — Fri, 30 Apr 2004 12:26:43 GMT

!!! I would check with Oracle before running the time backwards with an instance up!!! Especially if you are running in Online Archive mode...

Re: MC/SG, NTP and "date -a"

A. Clay Stephenson — Fri, 30 Apr 2004 12:34:02 GMT

data -a is the correct command to use but it will take quite a while to make up this difference. Date -a is perfecrtly safe to use
even with databases because it doesn't actually set time backwards. It allows the local clock to "tick" more slowly until the real world "catches up". Time continutes to march forward so that all database timestamps while not necessarily accurate are logically consistant. You are too far out of sync at the moment for NTP to operate.

Re: MC/SG, NTP and "date -a"

A. Clay Stephenson — Fri, 30 Apr 2004 12:34:04 GMT

date -a is the correct command to use but it will take quite a while to make up this difference. Date -a is perfecrtly safe to use
even with databases because it doesn't actually set time backwards. It allows the local clock to "tick" more slowly until the real world "catches up". Time continutes to march forward so that all database timestamps while not necessarily accurate are logically consistant. You are too far out of sync at the moment for NTP to operate.

Re: MC/SG, NTP and "date -a"

Abhik Sarkar_1 — Wed, 05 May 2004 09:06:43 GMT

Hi everyone,

Thanks for your answers and comments. Though I am still waiting for the customer's final confirmation that the time is OK, I checked this morning and I think that it's fine.

Thanks again,
Abhik.