If one component in a redundant pair is offline or powered off, host access to volumes
can be disrupted. Before you remove or power off a node canister or enclosure, verify whether any
volumes depend on those components.
The following examples describe scenarios where the system or node status can impact if a volume
is available to a host.
- If a control enclosure has only one node canister online, access to a volume depends on the
online node canister. For example, a host might lose access to a volume that is stored partially or
wholly on an array that uses drives in the offline node or its expansion enclosures.
- If one expansion canister in an expansion enclosure is powered off, further
expansion canisters to that down side chain get isolated from the control canister of the side
chain. In this case, host access to volumes depends on the online canister if the volume uses drives
in an isolated enclosure or the enclosure with the offline canister.
- If an entire expansion enclosure is powered off, both sides of the SAS
chain are broken. In this case, host access to some volumes can be considered to depend on the
entire expansion enclosure.
The impact that a service procedure might have on host access to data can be understood by using
the management GUI. To do so, use the following procedure:
- In the management GUI, select .
- On the System Hardware - Overview page, use the directional arrow near
the enclosure that contains the node canister to open the Enclosure Details
page.
- Under Rear View of the system, right-click the canister and select
Dependent Volumes from the Actions menu to display all
volumes that become disabled to hosts if the canister is powered off.
During a maintenance procedure, if the Dependent Volumes action identifies
dependent volumes, you may choose to stop the procedure. Then, investigate whether it is possible to
reinstate the redundancy in the system to carry out the procedure without loss of access to data.
For example, first complete procedures to ensure that both canisters in the enclosure are online.
Then, complete any procedure that powers off the only online canister in the enclosure.