vdsm hosts clock sync

[Shahar Havivi]

Hi,

I want to add a new feature that reports migration actual downtime (the time
that the VM was inaccessible to the user).

Libvirt reports that information but the vdsm hosts need to be in sync by clock
time.
I can measure the ping for NTP server an report back to the user if the ping
is too long (more then ~100ms or so) - a way to do that is via ntpstat shell
command.
The NTP delay can be report back via vdsStats and can be performed every
few hours or so.

Anyone knows of a better way that we can sync between hosts?

Thank you,
  Shahar Havivi.

[Alon Bar-Lev]

----- Original Message -----
>  From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  To: vdsm-devel(a)lists.fedorahosted.org
>  Sent: Monday, April 6, 2015 2:44:06 PM
>  Subject: [vdsm] vdsm hosts clock sync
>  
>  Hi,
>  
>  I want to add a new feature that reports migration actual downtime (the time
>  that the VM was inaccessible to the user).
>  
>  Libvirt reports that information but the vdsm hosts need to be in sync by
>  clock
>  time.
>  I can measure the ping for NTP server an report back to the user if the ping
>  is too long (more then ~100ms or so) - a way to do that is via ntpstat shell
>  command.
>  The NTP delay can be report back via vdsStats and can be performed every
>  few hours or so.
>  
>  Anyone knows of a better way that we can sync between hosts? 
I am unsure how a ping to clock source is helping, can you please explain more?

If you assume clocks are synced why anything more is needed?

Or would you like to have a solution in which you do not require clock sync?

>  
>  Thank you,
>    Shahar Havivi.
>  _______________________________________________
>  vdsm-devel mailing list
>  vdsm-devel(a)lists.fedorahosted.org
>  https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>

[Shahar Havivi]

On 06.04.15 07:50, Alon Bar-Lev wrote:
>  
>  
>  ----- Original Message -----
>  > From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  > To: vdsm-devel(a)lists.fedorahosted.org
>  > Sent: Monday, April 6, 2015 2:44:06 PM
>  > Subject: [vdsm] vdsm hosts clock sync
>  > 
>  > Hi,
>  > 
>  > I want to add a new feature that reports migration actual downtime (the time
>  > that the VM was inaccessible to the user).
>  > 
>  > Libvirt reports that information but the vdsm hosts need to be in sync by
>  > clock
>  > time.
>  > I can measure the ping for NTP server an report back to the user if the ping
>  > is too long (more then ~100ms or so) - a way to do that is via ntpstat shell
>  > command.
>  > The NTP delay can be report back via vdsStats and can be performed every
>  > few hours or so.
>  > 
>  > Anyone knows of a better way that we can sync between hosts?
>  
>  I am unsure how a ping to clock source is helping, can you please explain more? 
In
this case I can only report back to the user that its hosts clock is
delayed and need to be set...
>  
>  If you assume clocks are synced why anything more is needed? 
Why do I assume that?
>  
>  Or would you like to have a solution in which you do not require clock sync? 
I do
need the clock to be in sync - if not libvirts "actual downtime
migration" will be not accurate.

>  
>  > 
>  > Thank you,
>  >   Shahar Havivi.
>  > _______________________________________________
>  > vdsm-devel mailing list
>  > vdsm-devel(a)lists.fedorahosted.org
>  > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>  >

[Alon Bar-Lev]

----- Original Message -----
>  From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  To: "Alon Bar-Lev" <alonbl(a)redhat.com&gt;
>  Cc: vdsm-devel(a)lists.fedorahosted.org
>  Sent: Monday, April 6, 2015 2:54:07 PM
>  Subject: Re: [vdsm] vdsm hosts clock sync
>  
>  On 06.04.15 07:50, Alon Bar-Lev wrote:
>  > 
>  > 
>  > ----- Original Message -----
>  > > From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  > > To: vdsm-devel(a)lists.fedorahosted.org
>  > > Sent: Monday, April 6, 2015 2:44:06 PM
>  > > Subject: [vdsm] vdsm hosts clock sync
>  > > 
>  > > Hi,
>  > > 
>  > > I want to add a new feature that reports migration actual downtime (the
>  > > time
>  > > that the VM was inaccessible to the user).
>  > > 
>  > > Libvirt reports that information but the vdsm hosts need to be in sync by
>  > > clock
>  > > time.
>  > > I can measure the ping for NTP server an report back to the user if the
>  > > ping
>  > > is too long (more then ~100ms or so) - a way to do that is via ntpstat
>  > > shell
>  > > command.
>  > > The NTP delay can be report back via vdsStats and can be performed every
>  > > few hours or so.
>  > > 
>  > > Anyone knows of a better way that we can sync between hosts?
>  > 
>  > I am unsure how a ping to clock source is helping, can you please explain
>  > more?
>  In this case I can only report back to the user that its hosts clock is
>  delayed and need to be set...
>  > 
>  > If you assume clocks are synced why anything more is needed?
>  Why do I assume that?
>  > 
>  > Or would you like to have a solution in which you do not require clock
>  > sync?
>
>  I do need the clock to be in sync - if not libvirts "actual downtime
>  migration" will be not accurate. 
you do not need clock to sync, you need to know the delta between hosts.

but if you assume clock are in sync so what is the actual question?

>  
>  > 
>  > > 
>  > > Thank you,
>  > >   Shahar Havivi.
>  > > _______________________________________________
>  > > vdsm-devel mailing list
>  > > vdsm-devel(a)lists.fedorahosted.org
>  > > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>  > > 
>

[Shahar Havivi]

On 06.04.15 08:00, Alon Bar-Lev wrote:
>  
>  
>  ----- Original Message -----
>  > From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  > To: "Alon Bar-Lev" <alonbl(a)redhat.com&gt;
>  > Cc: vdsm-devel(a)lists.fedorahosted.org
>  > Sent: Monday, April 6, 2015 2:54:07 PM
>  > Subject: Re: [vdsm] vdsm hosts clock sync
>  > 
>  > On 06.04.15 07:50, Alon Bar-Lev wrote:
>  > > 
>  > > 
>  > > ----- Original Message -----
>  > > > From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  > > > To: vdsm-devel(a)lists.fedorahosted.org
>  > > > Sent: Monday, April 6, 2015 2:44:06 PM
>  > > > Subject: [vdsm] vdsm hosts clock sync
>  > > > 
>  > > > Hi,
>  > > > 
>  > > > I want to add a new feature that reports migration actual downtime (the
>  > > > time
>  > > > that the VM was inaccessible to the user).
>  > > > 
>  > > > Libvirt reports that information but the vdsm hosts need to be in sync by
>  > > > clock
>  > > > time.
>  > > > I can measure the ping for NTP server an report back to the user if the
>  > > > ping
>  > > > is too long (more then ~100ms or so) - a way to do that is via ntpstat
>  > > > shell
>  > > > command.
>  > > > The NTP delay can be report back via vdsStats and can be performed every
>  > > > few hours or so.
>  > > > 
>  > > > Anyone knows of a better way that we can sync between hosts?
>  > > 
>  > > I am unsure how a ping to clock source is helping, can you please explain
>  > > more?
>  > In this case I can only report back to the user that its hosts clock is
>  > delayed and need to be set...
>  > > 
>  > > If you assume clocks are synced why anything more is needed?
>  > Why do I assume that?
>  > > 
>  > > Or would you like to have a solution in which you do not require clock
>  > > sync?
>  >
>  > I do need the clock to be in sync - if not libvirts "actual downtime
>  > migration" will be not accurate.
>  
>  you do not need clock to sync, you need to know the delta between hosts.
>  
>  but if you assume clock are in sync so what is the actual question? 
As I understand
from your answer is by having configured ntp the hosts clock
are in sync.
>  
>  > 
>  > > 
>  > > > 
>  > > > Thank you,
>  > > >   Shahar Havivi.
>  > > > _______________________________________________
>  > > > vdsm-devel mailing list
>  > > > vdsm-devel(a)lists.fedorahosted.org
>  > > > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>  > > > 
>  >

On 6 Apr 2015, at 14:05, Shahar Havivi wrote:

>  On 06.04.15 08:00, Alon Bar-Lev wrote:
> > 
> > 
> > ----- Original Message -----
> >> From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
> >> To: "Alon Bar-Lev" <alonbl(a)redhat.com&gt;
> >> Cc: vdsm-devel(a)lists.fedorahosted.org
> >> Sent: Monday, April 6, 2015 2:54:07 PM
> >> Subject: Re: [vdsm] vdsm hosts clock sync
> >> 
> >> On 06.04.15 07:50, Alon Bar-Lev wrote:
> >>> 
> >>> 
> >>> ----- Original Message -----
> >>>> From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
> >>>> To: vdsm-devel(a)lists.fedorahosted.org
> >>>> Sent: Monday, April 6, 2015 2:44:06 PM
> >>>> Subject: [vdsm] vdsm hosts clock sync
> >>>> 
> >>>> Hi,
> >>>> 
> >>>> I want to add a new feature that reports migration actual downtime (the
> >>>> time
> >>>> that the VM was inaccessible to the user).
> >>>> 
> >>>> Libvirt reports that information but the vdsm hosts need to be in sync
> by
> >>>> clock
> >>>> time.
> >>>> I can measure the ping for NTP server an report back to the user if the
> >>>> ping
> >>>> is too long (more then ~100ms or so) - a way to do that is via ntpstat
> >>>> shell
> >>>> command.
> >>>> The NTP delay can be report back via vdsStats and can be performed every
> >>>> few hours or so.
> >>>> 
> >>>> Anyone knows of a better way that we can sync between hosts?
> >>> 
> >>> I am unsure how a ping to clock source is helping, can you please explain
> >>> more?
> >> In this case I can only report back to the user that its hosts clock is
> >> delayed and need to be set… 
I had in mind that hosts are synchronized by NTP and we report the difference between
local time and the reference (NTP) time, i.e. what "ntpstat" returns
This way we don't need to ping around or compare directly all the hosts, but we can
rely on the same source and individual hosts's awareness of accuracy

> >>> 
> >>> If you assume clocks are synced why anything more is needed?
> >> Why do I assume that? 
the feature requires those 2 hosts to have same clock, not necessarily the correct one.
But I believe having all hosts sync to the actual time is beneficial on its own

> >>> 
> >>> Or would you like to have a solution in which you do not require clock
> >>> sync?
> >> 
> >> I do need the clock to be in sync - if not libvirts "actual downtime
> >> migration" will be not accurate.
> > 
> > you do not need clock to sync, you need to know the delta between hosts. 
the libvirt API uses the delta internally so we can't use only that. Also I think it
is easier to have clock synced by a tool designated for that

> > 
> > but if you assume clock are in sync so what is the actual question?
>  As I understand from your answer is by having configured ntp the hosts clock
>  are in sync. 
we need to report that they are sync and how off the actual local clock is

Thanks,
michal

> > 
> >> 
> >>> 
> >>>> 
> >>>> Thank you,
> >>>>  Shahar Havivi.
> >>>> _______________________________________________
> >>>> vdsm-devel mailing list
> >>>> vdsm-devel(a)lists.fedorahosted.org
> >>>> https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
> >>>> 
> >> 
>  _______________________________________________
>  vdsm-devel mailing list
>  vdsm-devel(a)lists.fedorahosted.org
>  https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>  
>

[Alon Bar-Lev]

----- Original Message -----
>  From: "Michal Skrivanek"
> <michal.skrivanek(a)redhat.com&gt;
>  To: "Shahar Havivi" <shaharh(a)redhat.com&gt;, "Alon Bar-Lev"
> <alonbl(a)redhat.com&gt;
>  Cc: vdsm-devel(a)lists.fedorahosted.org
>  Sent: Monday, April 6, 2015 4:31:44 PM
>  Subject: Re: [vdsm] vdsm hosts clock sync
>  
>  
>  On 6 Apr 2015, at 14:05, Shahar Havivi wrote:
>  
>  > On 06.04.15 08:00, Alon Bar-Lev wrote:
>  >> 
>  >> 
>  >> ----- Original Message -----
>  >>> From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  >>> To: "Alon Bar-Lev" <alonbl(a)redhat.com&gt;
>  >>> Cc: vdsm-devel(a)lists.fedorahosted.org
>  >>> Sent: Monday, April 6, 2015 2:54:07 PM
>  >>> Subject: Re: [vdsm] vdsm hosts clock sync
>  >>> 
>  >>> On 06.04.15 07:50, Alon Bar-Lev wrote:
>  >>>> 
>  >>>> 
>  >>>> ----- Original Message -----
>  >>>>> From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  >>>>> To: vdsm-devel(a)lists.fedorahosted.org
>  >>>>> Sent: Monday, April 6, 2015 2:44:06 PM
>  >>>>> Subject: [vdsm] vdsm hosts clock sync
>  >>>>> 
>  >>>>> Hi,
>  >>>>> 
>  >>>>> I want to add a new feature that reports migration actual downtime
> (the
>  >>>>> time
>  >>>>> that the VM was inaccessible to the user).
>  >>>>> 
>  >>>>> Libvirt reports that information but the vdsm hosts need to be in
> sync
>  >>>>> by
>  >>>>> clock
>  >>>>> time.
>  >>>>> I can measure the ping for NTP server an report back to the user if
> the
>  >>>>> ping
>  >>>>> is too long (more then ~100ms or so) - a way to do that is via
> ntpstat
>  >>>>> shell
>  >>>>> command.
>  >>>>> The NTP delay can be report back via vdsStats and can be performed
>  >>>>> every
>  >>>>> few hours or so.
>  >>>>> 
>  >>>>> Anyone knows of a better way that we can sync between hosts?
>  >>>> 
>  >>>> I am unsure how a ping to clock source is helping, can you please
>  >>>> explain
>  >>>> more?
>  >>> In this case I can only report back to the user that its hosts clock is
>  >>> delayed and need to be set…
>  
>  I had in mind that hosts are synchronized by NTP and we report the difference
>  between local time and the reference (NTP) time, i.e. what "ntpstat" returns
>  This way we don't need to ping around or compare directly all the hosts, but
>  we can rely on the same source and individual hosts's awareness of accuracy
>  
>  >>>> 
>  >>>> If you assume clocks are synced why anything more is needed?
>  >>> Why do I assume that?
>  
>  the feature requires those 2 hosts to have same clock, not necessarily the
>  correct one. But I believe having all hosts sync to the actual time is
>  beneficial on its own
>  
>  >>>> 
>  >>>> Or would you like to have a solution in which you do not require clock
>  >>>> sync?
>  >>> 
>  >>> I do need the clock to be in sync - if not libvirts "actual downtime
>  >>> migration" will be not accurate.
>  >> 
>  >> you do not need clock to sync, you need to know the delta between hosts.
>  
>  the libvirt API uses the delta internally so we can't use only that. Also I
>  think it is easier to have clock synced by a tool designated for that
>  
>  >> 
>  >> but if you assume clock are in sync so what is the actual question?
>  > As I understand from your answer is by having configured ntp the hosts
>  > clock
>  > are in sync.
>  
>  we need to report that they are sync and how off the actual local clock is 
once again, you have the solution so why ask the question?
you assume ntpd - please make sure it is actually configured.

>  
>  Thanks,
>  michal
>  
>  >> 
>  >>> 
>  >>>> 
>  >>>>> 
>  >>>>> Thank you,
>  >>>>>  Shahar Havivi.
>  >>>>> _______________________________________________
>  >>>>> vdsm-devel mailing list
>  >>>>> vdsm-devel(a)lists.fedorahosted.org
>  >>>>> https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>  >>>>> 
>  >>> 
>  > _______________________________________________
>  > vdsm-devel mailing list
>  > vdsm-devel(a)lists.fedorahosted.org
>  > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>  > 
>  > 
>  
>

I also did not understand if you assume that host are all synced
via ntp, meanning that you expect the user to configure it.
Anyway , even ntp synced servers has an order of 100ms drift between
them (which I assume in this case is perfectly acceptable).

Thanks,
Ido

----- Original Message -----
From: "Alon Bar-Lev" <alonbl(a)redhat.com&gt;
To: "Shahar Havivi" <shaharh(a)redhat.com&gt;
Cc: vdsm-devel(a)lists.fedorahosted.org
Sent: Monday, April 6, 2015 2:50:10 PM
Subject: Re: [vdsm] vdsm hosts clock sync



----- Original Message -----
>  From: "Shahar Havivi" <shaharh(a)redhat.com&gt;
>  To: vdsm-devel(a)lists.fedorahosted.org
>  Sent: Monday, April 6, 2015 2:44:06 PM
>  Subject: [vdsm] vdsm hosts clock sync
>  
>  Hi,
>  
>  I want to add a new feature that reports migration actual downtime (the time
>  that the VM was inaccessible to the user).
>  
>  Libvirt reports that information but the vdsm hosts need to be in sync by
>  clock
>  time.
>  I can measure the ping for NTP server an report back to the user if the ping
>  is too long (more then ~100ms or so) - a way to do that is via ntpstat shell
>  command.
>  The NTP delay can be report back via vdsStats and can be performed every
>  few hours or so.
>  
>  Anyone knows of a better way that we can sync between hosts? 
I am unsure how a ping to clock source is helping, can you please explain more?

If you assume clocks are synced why anything more is needed?

Or would you like to have a solution in which you do not require clock sync?

>  
>  Thank you,
>    Shahar Havivi.
>  _______________________________________________
>  vdsm-devel mailing list
>  vdsm-devel(a)lists.fedorahosted.org
>  https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
>   
_______________________________________________
vdsm-devel mailing list
vdsm-devel(a)lists.fedorahosted.org
https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel

[Sven Kieske]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

OT:

you should not use "vdsm-devel(a)lists.fedorahosted.org"
any more.
use devel(a)ovirt.org instead.

kind regards

Sven
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