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 -- 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 might choose to stop the procedure. You can then investigate
whether it is possible to reinstate the redundancy in the system so that the procedure can be
carried out without loss of access to data. For example, you first can complete procedures to ensure
that both canisters in the enclosure are online; then, you can complete any procedure that powers
off the only online canister in the enclosure.