Storage Provisioning: Storage Groups, Volumes, and Masking Views
Provisioning questions almost always come down to five objects and their relationships: volume, storage group (SG), initiator group (IG), port group (PG) and masking view (MV). Learn the rules that constrain those relationships, because most wrong answers break one of them.
The objects
- A volume is a thin device created in an SRP with a host-visible capacity and an emulation (FBA). Devices can be created standalone and added to a storage group later.
- A storage group is the unit of presentation and the unit that carries SLO and workload. A volume can belong to exactly one storage group.
- An initiator group holds host initiators: WWPNs for Fibre Channel, IQNs/NQNs for iSCSI and NVMe, with host flags (SPC2, AIX, VMware, Windows) that set SCSI behaviour.
- A port group lists front-end ports as director:port, ideally spread across directors and engines.
- A masking view joins one IG, one PG and one SG. A storage group can be in exactly one masking view, and the view is what actually presents LUNs to the host.
Order of work
Create the SG and add volumes, create the IG and add initiators, create the PG, then create the MV and let the array assign host LUN IDs (or set them manually, using consistent LUN IDs for clusters). Adding a volume to an SG that is already in a masking view presents it automatically.
Worked example
Four ESXi hosts must all see the same two 1 TB volumes. Do not try to attach four initiator groups to one masking view: a storage group can only be in one view. Either place all four hosts' initiators in a single IG and build one MV, or create four SGs and one MV per SG. For shared datastores, the single IG holding every host initiator is the usual design.
Traps
Adding a host WWN to two IGs that use the same port group; forgetting a volume must be in the SG before the MV presents it; assuming removing an MV deletes the volumes; and changing SLO on a production SG without checking compliance impact.