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This article describes how you can start a clustered SAP instance in emergency situations, for example, if you have huge problems with the cluster or the high availability solution in general.
Problem
You run a clustered ASCS instance of SAP NetWeaver or S/4 HANA in a Windows Failover cluster.
For some reason you're not able to bring either the SAP service cluster resource and/or the SAP instance cluster resource online.
You cannot start the ASCS instance on any cluster node, this is a system standstill situation.
Solution
You have saved all important logs for later inspection (cluster logs, \work folder of ASCS instance, Windows Event Viewer logs).
Open Windows Failover Cluster Manager tool and select Properties tab of SAP cluster resource. In this example, the SAP service cluster resource can be brought online, but the SAP instance resource is in failed state:
Enable the "Maintenance Mode" for this resource (0 = disabled, 1 = enabled):
You get the information that SAP is now "in maintenance":
The cluster will no longer start/stop or control the cluster resource "SAP RA1 00 Instance". You can now use SAP MMC or use commandline tool sapcontrol.exe to start/stop this instance:
The cluster will no longer do health checking and does not interfere with operations. This configuration is similar to a "non-clustered" ASCS instance.
Caution!
SAP MMC shows the ASCS instance and the whole system as "green" = started:
But in the Failover Cluster Manager you still see the SAP instance resource in state "failed"! The cluster will not detect the started or stopped instance, because it is still "in maintenance".
If you want to leave maintenance mode, then change the value back to "0". Depending on the status of the instance (started or stopped) this can lead to an interruption!
Recommendation
Stop ASCS instance in SAP MMC. Check the correct cluster node in Failover Cluster Manager! Then disable the maintenance mode of the instance resource (value = 0).
