VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
Upgrade path when not enough resources in the cluster
A common question is what is the recommended upgrade path for customers who
have overcommitted and do not have enough free space to do a full evacuation, for
example 3 node clusters?
The vsan.v2_ondisk_upgrade has an option called allow-reduced-redundancy. It
should be noted that there are risks associated with this approach but unfortunately
there is no other way to do the upgrade. For a portion of the upgrade, virtual
machines will be running without replica copies of the data, so any failure during
the upgrade can lead to virtual machine downtime.
When this option is used, the upgrade deletes and creating disk groups one at a time,
on each host, and then allows the components rebuild once the on-disk format is at
v2. When the operation has completed on the first host, it is repeat for the next host
and so on until all hosts in the cluster are running on-disk format v2. However
administrators need to be aware that their virtual machines could be running
unprotected for a period during this upgrade.
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