What is the impact of maintenance mode in a VSAN enabled cluster data recovery
A virtual storage area network (VSAN) is a collection of ports from sets of connected switches that form a virtual network in which network nodes interconnect via network switches. Ports within a single switch can be partitioned into multiple VSANs which share the same hardware. The use of VSANs enables isolation of data from a specific portion of the network thus if a problem occurs in one VSAN it can be dealt with without hurting the whole network.
Before shutting down, disconnecting or rebooting a VSAN cluster host, it’s a must you place the host in maintenance mode. When the host is put into maintenance mode, the cluster capacity is greatly reduced as the host no longer contributes capacity to the cluster. Placing the host into recovery mode has several impacts on the performance bit.
There are three ways which can be used to place a host storing the VSAN cluster into maintenance mode and each of them has some impacts.
Full data migration – This involves transferring all the data that is residing on the host. This is not the best option but will be chosen for a couple of reasons; if the host is being replaced by a new one, if you want to maintain its availability during the maintenance window or if the host will be down for a long time. IMPACT; it will take a long time to complete especially if there is more data to migrate. When the migration is completed, the host is therefore evacuated from the cluster and all data spread across the remaining hosts.
Ensure accessibility– This is to ensure that all VMs will remain accessible by migrating the required data to other hosts. By choosing the ensure accessibility option, VSANs generate single copies of data that they find and regenerate them on other hosts available. Therefore, when the host is placed in maintenance mode, all the VM data is available. This is actually the default selection and is the most used. IMPACT; Most of the available policies will be violated as some VMs will be running in a degraded state with a less copy as the policy specifies.
No data migration– This option puts the host in maintenance mode despite what is going on in the clusters. It is chosen if the cluster is completely healthy, or the VMs are completely powered off or the critical VMs won’t be impacted. IMPACT; Due to the failure to tolerate policy, you may find that some of the VMs are unusable.
Those are the impacts of each way of maintenance mode in a VSAN enabled cluster data recovery.