vSAN host fails to enter Maintenance Mode with 'Full data migration' option selected in a 4 node vSAN OSA Cluster
Article ID: 397437
Updated On:
Products
Issue/Introduction
During a vSAN host decommissioning, host fails to enter maintenance mode with full data migration option selected in a 4-node vSAN OSA cluster.
When entering Maintenance Mode a "What-if" scenario will be run. If the result is, that after entering Maintenance Mode only not enough Fault Domains will be available the Full Data migration will fail.
The clomd.log will provide the related error message:LOM_CheckClusterResourcesForPolicy: Not enough Upper FD's available. Available: 3, needed: 4
Environment
VMware vSAN 8.0.x OSA
VMware vSAN 7.0.x OSA
Cause
A host will fail to enter maintenance mode using full data migration if the cluster is not able to meet the minimum number of fault domains that the storage policy requires which is N+1.
If the RAID 5 policy is in use, It needs at least 4 node to be fully compliant
vSAN requires a certain number of hosts to be active with disk groups contributing capacity and resources in vSAN in order to provide fault tolerance. If the requirements cannot be met, vSAN will fail the pre-check it performs when placing a host into maintenance mode.
Resolution
To decommission one of the four hosts, change the policy of the Raid 5 objects to Raid 1 Policy before attempting to put host into Maintenance Mode with full data migration.
Additional Information
Please be aware that during the change from RAID5 to RAID1, new components will be created first and the old ones deleted once the rebuild has completed. Make sure that there is sufficient space in the cluster before proceeding.
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