VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
Failures: absent vs. degraded
Virtual SAN has 2 types of failure states for components: ABSENT and DEGRADED.
A component is DEGRADED if Virtual SAN has detected a failure from which
it believes the component will not return (e.g. a component residing on a
failed disk drive)
A component is ABSENT if Virtual SAN has detected a failure, but Virtual SAN
believes that the component may re-appear with all data intact (e.g. an ESXi
host has been rebooted, and thus all components on disks on that ESXi host
are impacted)
An ABSENT state reflects a transient situation that may or not resolve itself over
time, and a DEGRADED state is a permanent state.
It is interesting to note the difference between a disk that has been hot unplugged or
offlined and a disk that has actually failed, as shown above. Since the disk that was
unplugged or offlined may be reinserted or onlined, Virtual SAN treats the
components residing on such a disk as ABSENT. If a disk has a permanent failure,
the components are marked as DEGRADED.
When a component is marked as ABSENT, Virtual SAN will wait for 60 minutes (by
default) for the components to become available once again. If they do not, and the
timer expires, Virtual SAN will begin rebuilding the components elsewhere in the
cluster. DEGRADED components are rebuilt immediately.
Note that both ABSENT and DEGRADED are treated as a single failure by Virtual
SAN; neither has any more impact than the other when it comes to managing
failures-to-tolerate on the cluster. A component that is marked as ABSENT and a
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