5:53 p.m.
Has anyone tried mirroring or multimaster under VMware i.e. are the
virtual clocks stable enough? We're starting to use VMware to cut down on
the number of physical hosts, but I'd like to use the latest 2.4 features
as well.
--
Dave Horsfall DTM VK2KFU Ph: +61 2 9552-5509 (direct) +61 2 9552-5500 (switch)
Corinthian Eng'ng P/L, Ste 54 Jones Bay Whf, 26-32 Pirrama Rd, Pyrmont 2009, AU
6:21 p.m.
Dave Horsfall wrote:
Has anyone tried mirroring or multimaster under VMware i.e. are the
virtual clocks stable enough? We're starting to use VMware to cut down on
the number of physical hosts, but I'd like to use the latest 2.4 features
as well.
I don't have any long-term experience with that setup, just use VMware for
short-duration tests. My suspicion is that the clock stability isn't very
good, and ntpd can't correct for it...
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
2:51 a.m.
yes, there are issues with a clock in vmware virtual hosts. ntpd is not
a solution, the right way is to run ntpd on physical machine and set up
virtual machines to sync clock with the physical one (using vmware
tools)
M.
On Tue, 2008-07-29 at 18:21 -0700, Howard Chu wrote:
Dave Horsfall wrote:
> Has anyone tried mirroring or multimaster under VMware i.e. are the
> virtual clocks stable enough? We're starting to use VMware to cut down on
> the number of physical hosts, but I'd like to use the latest 2.4 features
> as well.
>
I don't have any long-term experience with that setup, just use VMware for
short-duration tests. My suspicion is that the clock stability isn't very
good, and ntpd can't correct for it...
3:28 a.m.
Martin Simovic wrote:
yes, there are issues with a clock in vmware virtual hosts. ntpd is
not
a solution, the right way is to run ntpd on physical machine and set up
virtual machines to sync clock with the physical one (using vmware
tools)
Even that is insufficient; the clock synchronization is neither continuous nor
deterministic so there are long periods of time where the virtual clocks drift
before they're corrected by the next sync.
M.
On Tue, 2008-07-29 at 18:21 -0700, Howard Chu wrote:
> Dave Horsfall wrote:
>> Has anyone tried mirroring or multimaster under VMware i.e. are the
>> virtual clocks stable enough? We're starting to use VMware to cut down on
>> the number of physical hosts, but I'd like to use the latest 2.4 features
>> as well.
>>
> I don't have any long-term experience with that setup, just use VMware for
> short-duration tests. My suspicion is that the clock stability isn't very
> good, and ntpd can't correct for it...
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
4:06 a.m.
On Wed, 30 Jul 2008, Howard Chu wrote:
Martin Simovic wrote:
> yes, there are issues with a clock in vmware virtual hosts. ntpd is
> not a solution, the right way is to run ntpd on physical machine and
> set up virtual machines to sync clock with the physical one (using
> vmware tools)
Even that is insufficient; the clock synchronization is neither
continuous nor deterministic so there are long periods of time where the
virtual clocks drift before they're corrected by the next sync.
So *that* explains the many critical NTP warnings that I get from Nagios
when I monitor the remote host/guest...
--
Dave Horsfall DTM VK2KFU Ph: +61 2 9552-5509 (direct) +61 2 9552-5500 (switch)
Corinthian Eng'ng P/L, Ste 54 Jones Bay Whf, 26-32 Pirrama Rd, Pyrmont 2009, AU
3:22 a.m.
Howard Chu wrote:
Dave Horsfall wrote:
> Has anyone tried mirroring or multimaster under VMware i.e. are the
> virtual clocks stable enough? We're starting to use VMware to cut down on
> the number of physical hosts, but I'd like to use the latest 2.4 features
> as well.
>
I don't have any long-term experience with that setup, just use VMware for
short-duration tests. My suspicion is that the clock stability isn't very
good, and ntpd can't correct for it...
Thinking about this some more - why would you ever do this? If you're
consolidating many physical servers into a single physical server, just run a
single slapd on the consolidated server. You'll have more RAM available and
much less overhead.
The only good reason to run multiple masters is when you actually have
multiple physical servers, and they're set up such that they won't typically
all fail at once (e.g., in geographically remote locations so that a disaster
in one location doesn't affect the others). If all of your servers are going
to just be in VMs running on the same machine, and they're all replicating
with each other, you have no hardware redundancy, so you may as well just run
a single slapd on the real machine.
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
6:53 a.m.
Howard Chu wrote:
Thinking about this some more - why would you ever do this? If
you're
consolidating many physical servers into a single physical server, just
run a single slapd on the consolidated server. You'll have more RAM
available and much less overhead.
You would do this if you had disparate data centers with virtual
infrastructure clusters in each data center where you required the
redundancy of multiple masters at each data center but did not want to
maintain disparate directories.
Where I'm from, people do not run a single ESX host, they run clusters
of ESX hosts with 20-40 virtual machines on each host with hundreds of
virtual machines in each cluster. The benefits are seen only with
multiple ESX hosts.
All the best,
--
Josh Miller, RHCE/VCP
Seattle, WA
Linux Solutions Provider
http://itsecureadmin.com/
3:48 p.m.
On Wed, 30 Jul 2008, Howard Chu wrote:
Thinking about this some more - why would you ever do this? If
you're
consolidating many physical servers into a single physical server, just
run a single slapd on the consolidated server. You'll have more RAM
available and much less overhead.
That's the point; I'm looking for arguments against it, should it ever
come to pass.
They're unlikely to all be on the same server of course, but I really
don't want them virtualised at all.
--
Dave Horsfall DTM VK2KFU Ph: +61 2 9552-5509 (direct) +61 2 9552-5500 (switch)
Corinthian Eng'ng P/L, Ste 54 Jones Bay Whf, 26-32 Pirrama Rd, Pyrmont 2009, AU
3:02 a.m.
Howard Chu wrote:
Howard Chu wrote:
> Dave Horsfall wrote:
>> Has anyone tried mirroring or multimaster under VMware i.e. are the
>> virtual clocks stable enough? We're starting to use VMware to cut
>> down on
>> the number of physical hosts, but I'd like to use the latest 2.4
>> features
>> as well.
>>
> I don't have any long-term experience with that setup, just use VMware
> for
> short-duration tests. My suspicion is that the clock stability isn't very
> good, and ntpd can't correct for it...
>
Thinking about this some more - why would you ever do this?
1. Separation of operational processes at machine-level.
2. Importing, exporting, cloning, taking snapshots of VMs (e.g. I'm
often preparing machines with VMWare workstation which are then imported
into GSX/ESX server.)
3. HA with ESX cluster setups.
...
If you're
consolidating many physical servers into a single physical server, just
run a single slapd on the consolidated server. You'll have more RAM
available and much less overhead.
Sometimes scaling up does not have the highest priority.
If all of
your servers are going to just be in VMs running on the same machine,
and they're all replicating with each other, you have no hardware
redundancy, so you may as well just run a single slapd on the real machine.
One of my customers is running a VMWare ESX cluster in two separate
datacenters. Very handy.
Ciao, Michael.
8:50 p.m.
Dave Horsfall wrote:
Has anyone tried mirroring or multimaster under VMware i.e. are the
virtual clocks stable enough? We're starting to use VMware to cut down on
the number of physical hosts, but I'd like to use the latest 2.4 features
as well.
I have several multi-master setups running under VMware 3.0.2 and have
been so for around 6 months without any issues. Timekeeping has not
been an issue.
--
Josh Miller - RHCE, VCP
Linux Solutions Provider
Seattle, WA USA
http://itsecureadmin.com/
3:09 a.m.
Dave Horsfall wrote:
Has anyone tried mirroring or multimaster under VMware i.e. are the
virtual clocks stable enough?
This very much depends on the hardware your host system is running on
and the guest OS you're using.
Example but without OpenLDAP:
I've prepared a VM running Debian Linux 4.0 Etch for a customer with
VMWare workstation on my old Linux notebook and had many time sync
problems running it locally. But I did not bother tweaking the guest OS'
kernel settings for solving this because in production it runs on a ESX
cluster on very fast hardware. No clock sync issues there at all. BTW:
It's using Kerberos so everybody would recognize a significant clock
skew. ;-)
There is clock sync information by VMWare.
Ciao, Michael.
4:35 p.m.
On Thu, 31 Jul 2008, Michael Ströder wrote:
This very much depends on the hardware your host system is running on
and the guest OS you're using.
Host is Ubuntu 8.04.1 on dual-core 3GHz Intel, 2Gb memory, and the guest
is FreeBSD 7.0. I know that none of this is officially supported, but I
had no say in it. The box is going to get more memory soon, as it can
barely support three virtual hosts.
[...]
There is clock sync information by VMWare.
The fix for a FreeBSD guest is "kern.hz=100". I've been monitoring the
host with Nagios, and I've seen the NTP clock drift by up to a minute
before re-syncing; probably not good for ordinary replication...
--
Dave Horsfall DTM VK2KFU Ph: +61 2 9552-5509 (direct) +61 2 9552-5500 (switch)
Corinthian Eng'ng P/L, Ste 54 Jones Bay Whf, 26-32 Pirrama Rd, Pyrmont 2009, AU
5598
days inactive
5604
days old
openldap-technical@openldap.org
11 comments
5 participants
participants (5)
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Dave Horsfall -
Howard Chu -
Josh Miller -
Martin Simovic -
Michael Ströder