When a mirror plex encounters irrecoverable errors, Veritas Volume Manager (VxVM) detaches the plex from the mirrored volume. By default, VxVM automatically reattaches the affected mirror plexes when the underlying failed disk or LUN becomes visible. When VxVM detects that the device is online, the VxVM volume components on the involved LUN are automatically recovered, and the mirrors become usable.
VxVM uses the DMP failed LUN probing to detect when the device has come online. The timing for a reattach depends on the dmp_restore_interval, which is a tunable parameter. The number of LUNs that have reconnected may also affect the time required before the plex is reattached.
When VxVM is installed or the system reboots, VxVM starts the vxattachd daemon. The vxattachd daemon handles automatic reattachment for both plexes and sites. Thevxattachd daemon also initiates the resynchronization process for a plex. After a plex is successfully reattached, vxattachd notifies root.
If the global detach policy is set, a storage failure from any node causes all plexes on that storage to be detached globally. When the storage is connected back to any node, the vxattachd daemon triggers reattaching the plexes on the master node only.
The automatic reattachment functionality is local to a node. When enabled on a node, all of the disk groups imported on the node are monitored. If the automatic reattachment functionality is disabled on a master node, the feature is disable on all shared disk groups and private disk groups imported on the master node.
The vxattachd daemon listens for "dmpnode online" events using vxnotify to trigger its operation. Therefore, an automatic reattachment is not triggered if the dmpnode online event is not generated when vxattachd is running. The following are typical examples:
In CVM, with active/passive arrays, if all nodes cannot agree on a common path to an array controller, a plex can get detached due to I/O failure. In these cases, the dmpnode will not get disabled. Therefore, after the connections are restored, a dmpnode online event is not generated and automatic plex reattachment is not triggered.