If one component in a redundant pair is offline or powered off, host access to volumes
depends on an enclosure or canister in the system.
- If a control enclosure only has one node canister online, access to a volume depends on the
online node canister if the volume is stored partially or wholly on an array that uses drives in the
control enclosure or its expansion enclosures.
- If one expansion canister in an expansion enclosure is powered off, any expansion canisters
further down that side of the chain become isolated from the control canister on that side of the
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 the left and the right side 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.
- 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 unavailable to hosts if the canister is powered off.
During a maintenance procedure, if the Dependent Volumes action
indicates that there are 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. An example would be to do procedures to ensure
that both canisters in the enclosure are online before doing another procedure that powers off the
only online canister in the enclosure.