RAID-5 objects not immediately converted from 2+1 scheme to 4+1 scheme after increasing or decreasing the number of nodes in a vSAN cluster.
Article ID: 405876
Updated On:
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Issue/Introduction
vSAN ESA introduced the Adaptive RAID-5 functionality which automatically reconfigures the scheme used for RAID-5 vSAN objects based on the number of available nodes in the cluster for improvements in space-usage.
Environment
vSAN 8.x
vSAN 9.x
Cause
The two different available RAID-5 schemes require a minimum amount of nodes for component placement and N+1 consideration accounted for to improve rebuild-resiliency e.g. a 4-node cluster will use 2+1 scheme whereas a 6-node (or higher) cluster will use 4+1 scheme.
When the number of nodes with available Storage Pools in a cluster is increased (e.g. from 4 nodes to 6 nodes) or decreased (e.g. from 6 nodes to 5 nodes), a 24-hour timer in CLOMD on the nodes is initiated, following expiration of this timer, the nodes will start converting RAID-5 objects from 2+1 scheme to 4+1 scheme (if node count increased) or 4+1 scheme to 2+1 scheme (if node count decreased).
Once initialised (24 hours after the change in number of nodes in the cluster), this process can take multiple hours to complete depending on the number of objects to be converted and performance capabilities of the cluster.
Resolution
No user intervention is required - after the 24 hour timer has expired, objects will automatically start being converted to the other scheme and can be monitored via the Resyncing Objects tab (these will show as 'Compliance' under Intent column).
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