Hello andvm,
"As long as they have no VM's running on them I can make life simpler by only working on one of them at a time. (MM with FDM to keep data always compliant)"
Enter Maintenance-Mode with either EA or FDM options migrates all VMs off the hosts as part of this process(including powered-off ones unless specified otherwise).
Depending on what you are doing (e.g. patching a host vs physically moving it) using FDM option is potentially overkill as this will take an order of magnitude longer and put additional wear on your disks. For short downtimes (e.g. updates/patches) the vast majority of vSAN customers tend to go with ensuring back-ups are current and then using MM EA.
Those that have a requirement (legal/contract/SLA etc.) to maintain redundancy during maintenance windows tend to have FTT=2 policies in use and thus still have FTT=1 during rolling updates - I cannot recall the last customer that was using FTT=1 and doing MM FDM for anything relatively simple/short for the above reasons.
"Keeping on the same subject how can I find exactly how many hosts failures can a specific cluster support whilst satisfying data compliance (Default vSAN storage)?"
This isn't necessarily going to be the same for all data in any one cluster e.g. you can have a mix of FTT=0, FTT=1 and FTT=2 data in the same cluster - I would advise with looking at what Storage Policies are in use in each cluster.
"Of course these failures will have to be at different times to avoid data loss."
A data Object can withstand as many current failures as it's FTT provides - if it has the resources (e.g. enough FDs, and usable space that doesn't violate the SP) to rebuild after a failure then really it can have as many non-concurrent failures as it has resources to rebuild.
Bob
