Disk ownership changes during HA takeover and MetroCluster switchover in a four-node MetroCluster configuration
The ownership of disks temporarily changes automatically during high availability and MetroCluster operations. It is helpful to know how the system tracks which node owns which disks.
In ONTAP, a controller module's unique system ID (obtained from a node's NVRAM card or NVMEM board) is used to identify which node owns a specific disk. Depending on the HA or DR state of the system, the ownership of the disk might temporarily change. If the ownership changes because of an HA takeover or a DR switchover, the system records which node is the original (called home
) owner of the disk, so that it can return the ownership after HA giveback or DR switchback. The system uses the following fields to track disk ownership:
- Owner
- Home owner
- DR Home owner
In the MetroCluster configuration, in the event of a switchover, a node can take ownership of an aggregate originally owned by nodes in the partner cluster. Such aggregates are referred to as cluster-foreign aggregates. The distinguishing feature of a cluster-foreign aggregate is that it is an aggregate not currently known to the cluster, and so the DR Home owner field is used to show that it is owned by a node from the partner cluster. A traditional foreign aggregate within an HA pair is identified by Owner and Home owner values being different, but the Owner and Home owner values are the same for a cluster-foreign aggregate; thus, you can identify a cluster-foreign aggregate by the DR Home owner value.
As the state of the system changes, the values of the fields change, as shown in the following table:
| Value during... | ||||
|---|---|---|---|---|
| Field | Normal operation | Local HA takeover | MetroCluster switchover | Takeover during switchover |
| Owner | ID of the node that has access to the disk. | ID of the HA partner, which temporarily has access to the disk. | ID of the DR partner, which temporarily has access to the disk. | ID of the DR auxiliary partner, which temporarily has access to the disk. |
| Home owner | ID of the original owner of the disk within the HA pair. | ID of the original owner of the disk within the HA pair. | ID of the DR partner, which is the Home owner in the HA pair during the switchover. | ID of the DR partner, which is the Home owner in the HA pair during the switchover. |
| DR Home owner | Empty | Empty | ID of the original owner of the disk within the MetroCluster configuration. | ID of the original owner of the disk within the MetroCluster configuration. |
The following illustration and table provide an example of how ownership changes, for a disk in node_A_1's disk pool1, physically located in cluster_B.
| MetroCluster state | Owner | Home owner | DR Home owner | Notes |
|---|---|---|---|---|
| Normal with all nodes fully operational. | node_A_1 | node_A_1 | not applicable | |
| Local HA takeover, node_A_2 has taken over disks belonging to its HA partner node_A_1. | node_A_2 | node_A_1 | not applicable | |
| DR switchover, node_B_1 has taken over disks belong to its DR partner, node_A_1. | node_B_1 | node_B_1 | node_A_1 | The original home node ID is moved to the DR Home owner field. After aggregate switchback or healing, ownership goes back to node_A_1. |
| In DR switchover and local HA takeover (double failure), node_B_2 has taken over disks belonging to its HA node_B_1. | node_B_2 | node_B_1 | node_A_1 | After giveback, ownership goes back to node_B_1. After switchback or healing, ownership goes back to node_A_1. |
| After HA giveback and DR switchback, all nodes fully operational. | node_A_1 | node_A_1 | not applicable |