The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →For a supported Exchange Server deployment with a healthy Database Availability Group (DAG), the practical way to limit patch-related interruption is to update one member at a time: move it into maintenance mode, install the applicable update, restart and validate it, then return it to service before moving on. A DAG can help preserve service during that process, but it cannot guarantee zero downtime; the result depends on your actual redundancy, capacity, database health, and client and application dependencies.
Choose the right update for your Exchange release
First identify the Exchange release and build on every server, then confirm the currently supported target and package applicability in Microsoft’s live Exchange Server updates page. Do not choose a package solely because it is the newest file you can find: applicability depends on the installed Exchange release and cumulative update (CU), and support status affects which updates are eligible.
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| Update type | What it does | What to verify before scheduling |
|---|---|---|
| Cumulative update (CU) | A cumulative, full build that includes changes from earlier CUs. Microsoft’s Exchange Server update FAQ describes CUs as generally released twice a year while Exchange is in Mainstream support; the live updates page describes the delivery model as 1–2 CUs per year. Treat those cadences as guidance, not a promise of a particular release date. | Confirm the supported target, release notes, prerequisites, test results, and a maintenance window. A CU is not an uninstallable rollback to the previous version. |
| Security update (SU) | Released as needed, commonly around Patch Tuesday, and applicable to particular Exchange releases and CUs. A newer SU for a given CU includes earlier SUs for that CU, according to Microsoft’s update FAQ. | Check that the SU matches the installed release and CU, and follow its instructions. After installation, use Health Checker to identify any further required actions. |
Microsoft recommends installing available security updates rather than deciding to skip them solely because a CVE severity score looks low: vulnerabilities can combine into attack chains. Check the current update information and support status each time you plan a change; package guidance and release tables can change.
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- Inventory the servers and builds. Run Microsoft Exchange Server Health Checker to identify missing CUs or SUs and any manual actions that remain. Include Exchange servers and Management Tools-only machines in the inventory.
- Confirm supportability and package choice. Compare the installed builds with Microsoft’s current updates page, then read the release notes and prerequisites for the intended CU or SU. Do not extrapolate one server’s applicability to another Exchange release or CU.
- Rehearse CU changes outside production. Microsoft recommends testing a CU in a non-production environment. Confirm tested, working backups of Exchange and Active Directory, and record customizations that may need to be reapplied after the update. Microsoft warns that a CU cannot be uninstalled to return to the previous version; uninstalling the CU removes Exchange from that server.
- Set a realistic window from your own topology. Microsoft’s CU upgrade guidance states an estimated completion time of 180 minutes. That is Microsoft’s estimate for completing a CU upgrade, not a measured outage duration or a guarantee for your environment. Use your rehearsal and operational requirements to set the actual window.
- Check readiness using local procedures. Before taking a member out of service, verify DAG and database health, active database placement, available capacity, client access, and application dependencies. Microsoft’s general guidance does not establish that any particular organization’s topology can sustain every maintenance action without user impact.
Update DAG members one at a time
Microsoft recommends using DAGs and placing servers being updated into maintenance mode for a graceful update process. Its documented sequence is maintenance mode, installation, return to production, and optional redistribution of active databases. Keep the process rolling: do not update every member at once, and do not proceed until the updated member has passed the checks your organization requires.
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- Choose one member and protect active workloads. When appropriate, perform a server switchover before shutting down a DAG member. Microsoft cautions that high-availability shutdown behavior does not guarantee lossless activation for every database.
- Put that member into maintenance mode. Follow Microsoft’s DAG management procedure for the installed Exchange version and your topology. This article does not prescribe version-specific commands because the release and configuration determine the appropriate procedure.
- Install the planned CU or applicable SU. Follow the package’s release notes and setup guidance. During an update on a DAG member, Microsoft says Exchange services and the Cluster service stop.
- Restart and validate the member. Microsoft recommends restarting before and after Exchange updates, even when Setup does not prompt for a restart. Check that the server has returned to a healthy state and can perform its intended role before proceeding.
- Return the member to production. Take it out of maintenance mode using the documented procedure. Once it is healthy, you may redistribute active database copies if needed to rebalance the DAG.
- Repeat for the next member. Microsoft advises against leaving DAG members on different Exchange versions for an extended period. Keep the mixed-version interval limited to the rolling update and confirm each member before continuing.
The maintenance-mode process reduces the risk of taking a member out of service in an uncontrolled way; it does not remove risk from an unhealthy or undersized DAG. If readiness checks show insufficient capacity or database health problems, pause rather than treating the maintenance sequence as a guarantee of continued service.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Validate the update and close the change
- Confirm Exchange services and the Cluster service are running as expected, and that the member has exited maintenance mode.
- Check database copy health, mail flow, client access, and the monitoring signals and application checks used by your organization.
- After an SU, run Exchange Server Health Checker again to identify any additional actions required.
- Record the resulting builds and any customizations restored or manual actions completed.
If an update fails, use Microsoft’s Exchange update repair documentation and SetupAssist guidance linked from the Exchange Server update FAQ rather than improvising rollback steps. A CU uninstall is not a supported way to restore the prior CU.
When your deployment is not a DAG
The rolling member-by-member sequence applies to DAG environments. A standalone server has no DAG member to carry its workload during maintenance, so this procedure cannot promise uninterrupted service for it. Use the organization’s approved outage and recovery plan, verify backups and dependencies, and choose a maintenance window based on a rehearsal appropriate to that server. The exact steps depend on the Exchange release and deployment; consult the applicable Microsoft release notes and update guidance rather than copying DAG instructions onto a non-DAG server.
Keep Management Tools-only machines current
Microsoft says Management Tools-only machines should also receive SUs to reduce incompatibility between management clients and servers. An on-premises server used only to manage Exchange objects still needs to be kept current. Microsoft also says the Hybrid Configuration Wizard does not need to be rerun after Exchange updates.
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