When a storage controller fails and vSAN components are marked as Degraded, the repair process is initiated only after the CLOM (Cluster Object Manager) Repair Delay Timer expires. This delay is intended to handle transient issues without causing unnecessary rebuilds. Immediate rebuilding does not take place; instead, the system waits to see if the problem resolves on its own before starting the repair.
When a disk group is marked as absent due to the removal of a cache disk in a vSAN cluster, it's important to quickly ensure that the VMs are compliant with the storage policy. With FTT=1 RAID 1, the vSAN cluster can tolerate the failure of one host or its components. Given that there are still three operational nodes, the optimal remediation step is to use the vSAN Health Check to retest and then repair the objects immediately. This will resynchronize the absent objects on the remaining available hosts in the cluster, making the VMs compliant as soon as possible.
The additional disk group would make this cluster an unsupported configuration. In vSAN clusters, all disk groups within a host should ideally have a consistent configuration, including the type and size of cache and capacity drives. Mixing different types of SSDs (such as NVMe and SAS) and having different cache sizes among disk groups can create performance issues and inconsistencies. VMware best practices recommend homogeneity in disk group configurations to ensure optimal performance and supportability.
On-disk format version 3.0 or later is required to support deduplication and compression, and enabling these features on an All-Flash vSAN cluster with existing data requires data evacuation and a disk format upgrade of all the disk groups.
For a vSAN Stretched Cluster, a 5ms RTT or less is required between the data sites, ensuring low latency for efficient data replication across sites. Additionally, the cluster can utilize either Layer 2 or Layer 3 communication for the vSAN network, providing flexibility in the network configuration that can match various network topologies.