Normal operation mode

Heartbeat transmission

The heartbeat signals transmitted through the cluster interconnect adapters and cables tell each filer the state of the other filer. This information is written to disks on each filer that the cluster monitor designates as mailbox disks. The disks provide redundancy.

Monitoring

The cluster monitor software monitors the heartbeat signal, commands from filers, and disk connections, and initiates a takeover under the following conditions:

• The operator initiates a takeover using the cf takeover command.
• The partner is determined to have stopped functioning due to a lack of heartbeat activity.
• The negotiated failover facility determines that one partner should take over the other because of a disk shelf failure.
• The partner power-on-self-test (POST) fails.

  Note
  If the filer that is not transmitting a heartbeat is rebooting, no takeover occurs.

Takeover might be disabled if NVRAM mirroring is not functioning.

Automatic takeover is disabled if the partner mailbox disks are not accessible.

NVRAM mirroring

Each filer dedicates half of its NVRAM to a synchronously updated copy of its partner's NVRAM. If a takeover occurs, the takeover filer uses the cluster data in the part of the NVRAM dedicated to the failed filer to ensure that no information is lost.

Time synchronization

Filer times can deviate from each other. A daemon updates the times on filers periodically to keep them synchronized.