This is a header 1

sequenceDiagram
    participant VM as Virtual Machine
    participant ESXi as ESXi Host
    participant NFS as NFS Server
    participant vCenter as vCenter Server

    %% Normal Operation
    VM->>ESXi: I/O Request (Read/Write)
    ESXi->>NFS: Send I/O Request
    NFS-->>ESXi: I/O Response
    ESXi-->>VM: I/O Complete
    Note over ESXi,NFS: Normal operation with NFSv3 datastore

    %% Loss of Connectivity
    NFS-xESXi: Network/Storage Failure (Paths Down)
    Note over ESXi: All Paths Down (APD) detected
    ESXi->>NFS: Retry I/O Request
    NFS-xESXi: No Response (Failure)
    ESXi->>ESXi: Start APD Timer (140s)
    Note over ESXi: APD Timer running, retries continue

    %% Retry Attempts During APD
    loop Every few seconds
        ESXi->>NFS: Retry I/O Request
        NFS-xESXi: No Response
    end
    Note over ESXi: I/O retries continue for 140s

    %% APD Timeout
    ESXi->>ESXi: APD Timeout (140s reached)
    ESXi->>VM: Fast Fail I/O (Operations Halted)
    Note over ESXi: Datastore marked as inaccessible
    ESXi->>vCenter: Log APD Event
    vCenter->>vCenter: Mark ESXi Host as Disconnected/Not Responding
    Note over vCenter: esx.problem.storage.apd.timeout logged

    %% Administrator Intervention
    Note over NFS: Admin resolves issue (e.g., network restored)
    NFS-->>ESXi: Connectivity Restored
    ESXi->>NFS: Rescan Storage Paths
    NFS-->>ESXi: Path Available
    Note over ESXi: Datastore becomes accessible

    %% Recovery
    ESXi->>vCenter: Update Datastore/Host Status
    vCenter->>vCenter: Mark Host as Connected
    ESXi->>VM: Resume I/O Operations
    VM->>ESXi: I/O Request
    ESXi->>NFS: Send I/O Request
    NFS-->>ESXi: I/O Response
    ESXi-->>VM: I/O Complete
    Note over ESXi,NFS: Normal operation restored