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Merge pull request #31846 from LizCasey/fixing-warnings
fixing sync errors
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articles/virtual-machines/linux/time-sync.md

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On stand-alone hardware, the Linux OS only reads the host hardware clock on boot. After that, the clock is maintained using the interrupt timer in the Linux kernel. In this configuration, the clock will drift over time. In newer Linux distributions on Azure, VMs can use the VMICTimeSync provider, included in the Linux integration services (LIS), to query for clock updates from the host more frequently.
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Virtual machine interactions with the host can also affect the clock. During [memory preserving maintenance](maintenance-and-updates.md#maintenance-not-requiring-a-reboot), VMs are paused for up to 30 seconds. For example, before maintenance begins the VM clock shows 10:00:00 AM and lasts 28 seconds. After the VM resumes, the clock on the VM would still show 10:00:00 AM, which would be 28 seconds off. To correct for this, the VMICTimeSync service monitors what is happening on the host and prompts for changes to happen on the VMs to compensate.
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Virtual machine interactions with the host can also affect the clock. During [memory preserving maintenance](maintenance-and-updates.md#maintenance-that-doesnt-require-a-reboot), VMs are paused for up to 30 seconds. For example, before maintenance begins the VM clock shows 10:00:00 AM and lasts 28 seconds. After the VM resumes, the clock on the VM would still show 10:00:00 AM, which would be 28 seconds off. To correct for this, the VMICTimeSync service monitors what is happening on the host and prompts for changes to happen on the VMs to compensate.
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Without time synchronization working, the clock on the VM would accumulate errors. When there is only one VM, the effect might not be significant unless the workload requires highly accurate timekeeping. But in most cases, we have multiple, interconnected VMs that use time to track transactions and the time needs to be consistent throughout the entire deployment. When time between VMs is different, you could see the following effects:
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articles/virtual-machines/windows/time-sync.md

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Azure hosts are synchronized to internal Microsoft time servers that take their time from Microsoft-owned Stratum 1 devices, with GPS antennas. Virtual machines in Azure can either depend on their host to pass the accurate time (*host time*) on to the VM or the VM can directly get time from a time server, or a combination of both.
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Virtual machine interactions with the host can also affect the clock. During [memory preserving maintenance](maintenance-and-updates.md#maintenance-not-requiring-a-reboot), VMs are paused for up to 30 seconds. For example, before maintenance begins the VM clock shows 10:00:00 AM and lasts 28 seconds. After the VM resumes, the clock on the VM would still show 10:00:00 AM, which would be 28 seconds off. To correct for this, the VMICTimeSync service monitors what is happening on the host and prompts for changes to happen on the VMs to compensate.
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Virtual machine interactions with the host can also affect the clock. During [memory preserving maintenance](maintenance-and-updates.md#maintenance-that-doesnt-require-a-reboot), VMs are paused for up to 30 seconds. For example, before maintenance begins the VM clock shows 10:00:00 AM and lasts 28 seconds. After the VM resumes, the clock on the VM would still show 10:00:00 AM, which would be 28 seconds off. To correct for this, the VMICTimeSync service monitors what is happening on the host and prompts for changes to happen on the VMs to compensate.
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The VMICTimeSync service operates in either sample or sync mode and will only influence the clock forward. In sample mode, which requires W32time to be running, the VMICTimeSync service polls the host every 5 seconds and provides time samples to W32time. Approximately every 30 seconds, the W32time service takes the latest time sample and uses it to influence the guest's clock. Sync mode activates if a guest has been resumed or if a guest's clock drifts more than 5 seconds behind the host's clock. In cases where the W32time service is properly running, the latter case should never happen.
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articles/virtual-machines/workloads/sap/high-availability-guide-rhel-pacemaker.md

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[2243692]:https://launchpad.support.sap.com/#/notes/2243692
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[1999351]:https://launchpad.support.sap.com/#/notes/1999351
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[virtual-machines-linux-maintenance]:../../linux/maintenance-and-updates.md#maintenance-not-requiring-a-reboot
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[virtual-machines-linux-maintenance]:../../linux/maintenance-and-updates.md#maintenance-that-doesnt-require-a-reboot
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> [!NOTE]
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> Pacemaker on Red Hat Enterprise Linux uses the Azure Fence Agent to fence a cluster node if required. A failover can take up to 15 minutes if a resource stop fails or the cluster nodes cannot communicate which each other anymore. For more information, read [Azure VM running as a RHEL High Availability cluster member take a very long time to be fenced, or fencing fails / times-out before the VM shuts down](https://access.redhat.com/solutions/3408711)

articles/virtual-machines/workloads/sap/high-availability-guide-suse-pacemaker.md

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[deployment-guide]:deployment-guide.md
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[dbms-guide]:dbms-guide.md
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[sap-hana-ha]:sap-hana-high-availability.md
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[virtual-machines-linux-maintenance]:../../linux/maintenance-and-updates.md#maintenance-not-requiring-a-reboot
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[virtual-machines-windows-maintenance]:../../windows/maintenance-and-updates.md#maintenance-not-requiring-a-reboot
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[virtual-machines-linux-maintenance]:../../linux/maintenance-and-updates.md#maintenance-that-doesnt-require-a-reboot
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[virtual-machines-windows-maintenance]:../../windows/maintenance-and-updates.md#maintenance-that-doesnt-require-a-reboot
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[sles-nfs-guide]:high-availability-guide-suse-nfs.md
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[sles-guide]:high-availability-guide-suse.md
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