VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
VM Accessibility: inaccessible vs. orphaned
A VM’s accessibility can also be dependent on which objects have been affected by a
failure. These states will only be observed if a VM’s objects have been setup to
tolerate X number of failures in the cluster, and the cluster suffers greater than X
number of failures.
If a VM’s state is reported as Inaccessible, it means that at least one object of the VM
is completely down (temporarily or permanently) so either there is no full mirror of
the object (the failures have impacted both mirrors), or less than 50% of the
components or votes are available (the failures have impacted a mirror and
witnesses).
If a VM’s state is reported as Orphaned, it may mean that neither vCenter Server nor
the ESXi host can monitor/track the VM, i.e. there is no read access to VM’s “.vmx”
file. From a Virtual SAN perspective, this could imply that the VM Home Namespace
is currently down, meaning that there is no full mirror of the object or less than 50%
of the components or votes that make up the VM Home Namespace are available.
There are other reasons why a VM may be orphaned, but a problem with the VM
Home Namespace could be one of them.
However it should be understood that this state is a transient, and not a permanent
state. As soon as the underlying issue has been rectified and once a full mirror copy
and more than 50% of an object’s components or votes become available, the virtual
machine would automatically exit this inaccessible or orphaned state and become
accessible once again.
Failure handling – Virtual SAN fail safe mechanism
There have been occasions where the storage I/O controller does not tell the ESXi
host that anything is wrong; rather the controller may simply stall I/O, and become
‘wedged’. There have also been cases when pulling disk drives isn’t handled well by
the controller. For these reasons Virtual SAN has it’s own fail-safe mechanism for
failure handling.
Virtual SAN handles this condition by placing its own timeout on in-flight I/O, which
is somewhere between 20-30 seconds. If the timeout expires (because the controller
is stalled), Virtual SAN will mark the devices associated with the timed out I/O as
DEGRADED.
If an I/O controller “wedged”, and the I/O was destined for a capacity layer device,
Virtual SAN marks this disk as DEGRADED. If the I/O was destined for a flash layer
device, Virtual SAN marks the device as DEGRADED. Over time, all of the devices
sitting behind this controller will also be marked as DEGRADED.
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