v.: 2020-09-04
Copyright of the European Union is effective (Copyright EU) (c) 2019 GENEREX Systems GmbH, Hamburg, Germany, All rights reserved
TEL +49(40)22692910 - EMAIL generex@generex.de - WEB www.generex.de (This and all other product datasheets are available for download.)
28
Special role: The witness server
Small vSAN systems lack the necessary resources to be able to independently adjust all data stocks.
To prevent problems with data synchronization in minimalist vSAN systems, a witness server is used:
This witness server acts as a stand-alone host in vSAN, but is not responsible for hosting and managing virtual machines - as
soon as hosts are unable to agree with the timeliness of their datasets, the witness server decides which host has to
synchronize the data.
The witness server can be both, a real physical machine with it's own hardware as well as a acting like physical host but running
within a virtual machine. The vSAN knots cannot see the difference between the different setup strategies of a witness server.
But this difference affects the RCCMD configuration:
If running a real witness server as a standalone machine:
In this case, assign the witness server and any hosts
that you want to shut down. The hosts will go into
maintenance mode accordingly:
- Shut down virtual machines
- The vCenter will perform the reSynch
- The hosts switch into maintenance mode
- The hardware can be switched off.
When using a virtual machine to run a witness server
If you run the witness server as a virtual machine in the vSAN, you must differ between the host on which the witness server is
stored and the witness server as a stand-alone host. Since the witness server acts like a host within the vSAN, it is perceived
and treated accordingly - The installation type does not matter:
While the host that maintains the virtual machine of the witness internally perceives only one virtual machine running "some kind
of system", it accepts the witness server as a standalone host and network node on the network. If the wrong IP address has
now been specified, the host responsible for the virtual machine will respond correctly:
- The host will stop running the virtual machine
- The host changes to Maintenance Mode
However, since the (albeit virtualized) witness server represents a full-fledged host and network node, it must consequently be
treated as a real host and put into maintenance mode before being turned off. Formally, you need two RCCMD appliances to
shut down a vSAN. If you use a virtualized witness server, you can use the second RCCMD to regularly switch off the host that
manages the virtual witness server.
To Next Page
Loading...
