v.: 2020-09-04
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24
Note
Appliance vs Appliance - What is the Virtual Machine and what is "the RCCMD client"
Basically, the two appliances do not differ from each other: Both are virtual machines. However, because you use two
appliances, the name of the virtual machine they run themselves on, will differ. Entering the name of the virtual machine will
prevent that an RCCMD client will shut down itself first. So, if you tell RCCMD 2 the name of his own virtual machine, it will
consider that RCCMD 1 is just another "guest VM" and will shut down it. When using a vSAN, the shutdown commands of the
CS141 will harmonize the shutdown behavior of both appliances.
if you use a vSAN, take care for the time windows required by the modified shutdown sequence
The reason for using a vSAN is to combine a maximum data redundancy with a most possible availability of servers:
Basically, there is no reason for a regular vSAN cluster shut down.
A complete shutdown is an emergency issue, and should be handled accordingly:
It is difficult to predict how much time the vCenter will take within a vSAN to bring the hosts into maintenance mode.
In principle, the vSAN shutdown will be performed in three steps:
Shutdown of all virtual machines
In this step, all virtual machines will shut down.
Post synchronization phase
At this stage, all hosts synchronize their current datasets.
Switching into maintenance mode
All virtual machines are shut down and the datasets are up to date. The hosts can be switched off.
The critical system stage is the post synchronization phase. This process is difficult to assess:
The maintenance mode can only be assumed as soon as the synchronization of the data between all hosts has been
completed. Unfortunately, this process is dynamic and the time needed to fulfill this process depends an the level of used
hardware, the number of virtual machines as well as the amount and type of data that exists within the virtual machines.
To make it trickier, this process takes place within the VSAN without any information about the current data synchronization
state - at some point, the hosts are in maintenance mode, which means that the process is complete.
However, available time is determined by the maximum operating time of the UPS:
RCCMD needs validated timer settings that not only use the calculated times for a shutdown but also respects the granted
uptime of the UPS:
Ensure this time window …
allows to shut down the vSAN in good times.
contains some extra time if the post synchronization phase suddenly needs more time than expected
stays within the security range of the UPS's uptime,
ensures a shut down of other hosts and clusters, too.
System critical note:
Before you start to configure the shutdown of your vSAN, the following information are mandatory:
1. an overview of the time window that a UPS can grant for an orderly shutdown?
2. How long do you need for a manual shutdown?
Please note:
Due to the fact a vSAN is sensitive to shut down fails a vSAN is technically a very system critical process that needs your
attention.
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