VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
What happens when the entire cluster network fails?
A failure of this nature will result is a complete network partition, with each host
residing in its own partition. To an isolated host, it will look like all the other hosts
have failed. Behavior is similar to what was described in the previous section, but in
this case, since no quorum can be achieved for any object, no rebuilding takes place.
When the network issue is resolved, Virtual SAN will first establish a new cluster
and components will start to resync. Since the whole cluster was down, there won’t
have been many changes, but Virtual SAN ensures that components are
synchronized against the latest, most up to date copy of a component.
What happens when a storage I/O controller fails?
If a controller in a single controller configuration fails with a permanent failure, then
every disk group on the host will be impacted. This condition should be reasonably
easy to diagnose. The behavior of Virtual SAN when a storage I/O controller fails
will be similar to having all-flash cache devices and all disks fail in all disk groups. As
described above, components will be marked as DEGRADED in this situation
(permanent error) and component rebuilding should be immediate.
It might be difficult to determine if there is a flash cache device failure or a storage
I/O controller failure in a single controller configuration, where there is also only
one disk group with one flash device in the host. Both failures impact the whole disk
group. The VMkernel log files on the ESXi host may be able to assist with locating
the root cause. Also, leveraging third party tools from the controller vendor to query
the status of the hardware might be helpful.
If there are multiple disk groups on a host with a single controller, and all devices in
both disk groups are impacted, then you might assume that the common controller
is a root cause.
If there is a single disk group on a host with a single controller, and all devices in
that disk group are impacted, additional research will be necessary to determine if
the storage I/O controller is the culprit, or if it is the flash cache device that is at
fault.
Lastly, if there are multiple controllers on the host, and only the devices sitting
behind one controller is impacted, then you might assume that this controller is a
root cause.
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