VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
What happens when a disk fails?
Virtual SAN marks the disk as DEGRADED as the failure is permanent.
Expected behaviors:
If the VM has a policy that includes NumberOfFailuresToTolerate=1 or greater,
the VM’s objects will still be accessible.
The disk state is marked as DEGRADED and can be verified via vSphere web
client UI.
At this point, all in-flight I/O is halted while Virtual SAN reevaluates the
availability of the object without the failed component as part of the active
set of components.
If Virtual SAN concludes that the object is still available (based on available
full mirror copy and witness), all in-flight I/O is restarted.
The typical time from physical removal of the drive, Virtual SAN processing
this event, marking the component DEGRADED halting and restoring I/O
flow is approximately 5-7 seconds.
Virtual SAN now looks for any hosts and disks that can satisfy the object
requirements. This includes adequate free disk space and placement rules
(e.g. 2 mirrors may not share the same hosts/fault domains). If such
resources are found, Virtual SAN will create new components on there and
start the recovery process immediately.
If the VM Storage Policy has NumberOfFailuresToTolerate=0, the VMDK will
be inaccessible if one of the VMDK components (think one component of a
stripe) exists on the pulled disk. This will require a restore of the VM from a
known good backup.
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