NTP server periodically desyncs

Some time ago our NTP server (on Win SBS 2011 Std) started to desync occasionally. It can get 8 minutes slow overnight. Then after running w32tm /resync /rediscover it works fine for some time.
Configuration and status output (sorry that some of it is messed up. SBS doesn't allow changing the output language once it's been set up):
PS C:\Windows\system32> w32tm /query /configuration /verbose
[¿¿¿¿¿¿¿¿¿]

EventLogFlags: 2 (¿¿¿¿¿¿¿¿)
AnnounceFlags: 5 (¿¿¿¿¿¿¿¿)
TimeJumpAuditOffset: 28800 (¿¿¿¿¿¿¿¿)
MinPollInterval: 6 (¿¿¿¿¿¿¿¿)
MaxPollInterval: 10 (¿¿¿¿¿¿¿¿)
MaxNegPhaseCorrection: 3600 (¿¿¿¿¿¿¿¿)
MaxPosPhaseCorrection: 3600 (¿¿¿¿¿¿¿¿)
MaxAllowedPhaseOffset: 300 (¿¿¿¿¿¿¿¿)

FrequencyCorrectRate: 4 (¿¿¿¿¿¿¿¿)
PollAdjustFactor: 5 (¿¿¿¿¿¿¿¿)
LargePhaseOffset: 50000000 (¿¿¿¿¿¿¿¿)
SpikeWatchPeriod: 900 (¿¿¿¿¿¿¿¿)
LocalClockDispersion: 10 (¿¿¿¿¿¿¿¿)
HoldPeriod: 5 (¿¿¿¿¿¿¿¿)
PhaseCorrectRate: 7 (¿¿¿¿¿¿¿¿)
UpdateInterval: 100 (¿¿¿¿¿¿¿¿)

FileLogName:  (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
FileLogEntries:  (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
FileLogSize: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
FileLogFlags: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)

[TimeProviders]

NtpClient (¿¿¿¿¿¿¿¿)
DllName: C:\Windows\system32\w32time.dll (¿¿¿¿¿¿¿¿)
Enabled: 1 (¿¿¿¿¿¿¿¿)
InputProvider: 1 (¿¿¿¿¿¿¿¿)
CrossSiteSyncFlags: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
AllowNonstandardModeCombinations: 1 (¿¿¿¿¿¿¿¿)
ResolvePeerBackoffMinutes: 15 (¿¿¿¿¿¿¿¿)
ResolvePeerBackoffMaxTimes: 7 (¿¿¿¿¿¿¿¿)
CompatibilityFlags: 2147483648 (¿¿¿¿¿¿¿¿)
EventLogFlags: 1 (¿¿¿¿¿¿¿¿)
LargeSampleSkew: 3 (¿¿¿¿¿¿¿¿)
SpecialPollInterval: 900 (¿¿¿¿¿¿¿¿)
Type: NTP (¿¿¿¿¿¿¿¿)
NtpServer: time.windows.com,0x1 (¿¿¿¿¿¿¿¿)

NtpServer (¿¿¿¿¿¿¿¿)
DllName: C:\Windows\system32\w32time.dll (¿¿¿¿¿¿¿¿)
Enabled: 1 (¿¿¿¿¿¿¿¿)
InputProvider: 0 (¿¿¿¿¿¿¿¿)
AllowNonstandardModeCombinations: 1 (¿¿¿¿¿¿¿¿)
EventLogFlags: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)

VMICTimeProvider (¿¿¿¿¿¿¿¿)
DllName: C:\Windows\System32\vmictimeprovider.dll (¿¿¿¿¿¿¿¿)
Enabled: 1 (¿¿¿¿¿¿¿¿)
InputProvider: 1 (¿¿¿¿¿¿¿¿)

Open in new window

PS C:\Windows\system32> w32tm /query /status /verbose
¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿: 0(¿¿¿¿¿¿¿¿¿¿¿¿¿¿ ¿¿¿)
¿¿¿¿¿¿: 3 (¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿ - ¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿ ¿ ¿¿¿¿¿¿¿ (S)NTP)
¿¿¿¿¿¿¿¿: -6 (15.625ms ¿¿ ¿¿¿¿ ¿¿¿¿¿¿¿)
¿¿¿¿¿¿¿¿ ¿¿¿¿¿: 0.2534276s
¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿: 6.2850124s
ReferenceId: 0x40040A21 (IP-¿¿¿¿¿ ¿¿¿¿¿¿¿¿¿:  64.4.10.33)
Last Successful Sync Time: 05.06.2013 9:19:51
Source: time.windows.com,0x1
¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿: 6 (64s)

¿¿¿¿¿¿¿¿ ¿¿¿¿: 0.0000678s
¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿¿: 0.0156121s
¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿¿: 3 (¿¿¿¿¿)
¿¿¿¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿¿: 0 (¿¿¿)
Server Role: 576 (¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿ ¿¿¿¿¿¿¿)
Last Sync Error: 2 (The computer did not resync because only stale time data was available.)
Time since Last Good Sync Time: 162.4468032s

Open in new window

It says Last Successful Sync Time: 05.06.2013 9:19:51 but I checked shortly after this time and it was 8 minutes slow. Yesterday everything was okay. The server is the only time server and DC in our domain.
Why does this happen?
Thank you.
LVL 1
PavelTMNAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Nagendra Pratap SinghDesktop Applications SpecialistCommented:
Is it virtual?

Do you have any other time-sync tools installed on it?
0
PavelTMNAuthor Commented:
No, it's not virtual and there aren't any time-sync tools except built-in ones.
0
frankhelkCommented:
Hmm - I've had hassle with W32time in NTP mode whenever I used it.

My recommendation would be to just disable W32time and use "the real thing" - a Windows port of the standard NTP implementation. See here for a list.

Furthermore I would recommend to use the service at pool.ntp.org for a selection of time servers. Try these time server entries in your ntp.conf:
server 0.pool.ntp.org iburst
server 1.pool.ntp.org iburst
server 2.pool.ntp.org iburst
server 3.pool.ntp.org iburst

Open in new window

0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
PavelTMNAuthor Commented:
I would recommend to use the service at pool.ntp.org
I changed the NTP server to one suggested by you and so far the errors have disappeared along with skewing.
w32tm /config /syncfromflags:manual /manualpeerlist:3.ru.pool.ntp.org
w32tm /config /update
w32tm /resync
0
frankhelkCommented:
Just to improve the quality of the NTP service even further, I would recommend to supply more server entries. That way W32time (if you persist to cling to it ...) or ntpd (the native NTP daemon) would be able to choose the best time source from a group of servers.

Just try

w32tm /config /syncfromflags:manual /manualpeerlist:0.ru.pool.ntp.org,1.ru.pool.ntp.org,2.ru.pool.ntp.org,3.ru.pool.ntp.org
w32tm /config /update
w32tm /resync

Open in new window

0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Microsoft Server OS

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.