ServerNet States Help

The following topics are covered:

NonStop Cluster ServerNet SAN Overview

When the cluster boots, the NonStop Clusters environment on each node begins communications over the ServerNet SAN to form the cluster and verify that the X and Y paths to the other nodes are functioning properly. All nodes normally come up using the X path as shown in the figure. If a node initially detects errors on the X path, it comes up using the Y path. When the ServerNet Agent is started during the boot process, it sets all paths to the preferred paths (see  Designating a Preferred Path for more on preferred paths).

With the cluster up and running, the ServerNet SAN path used by each node will not change unless the SPA driver (SPAD) determines a path has failed or the path is switched manually, such as with the ServerNet States view. If the SPAD determines a path has failed (due to link exception conditions, a timeout on a ServerNet SAN packet, or for other reasons), it logs an error to the console and system log and switches the node to the other (Y or X) path. If running, the ServerNet Manager displays a dialog box to alert the user to the failure.
 

Terminology

The following basic terms apply to the NonStop Cluster ServerNet SAN and the ServerNet States view: Since there are X and Y fabrics, there are X and Y paths between any two end nodes in the cluster. The current path is the path being used for communications. A preferred path can be designated between any two end nodes to establish a default path used to balance traffic (tune performance) between the fabrics.

The path and fabric resources have operational and usage states associated with them. The fabric resource also has an availability status. The following table shows the values associated with the states and statuses and what they mean for the path and fabric resources.
 
State/Status Type
State/Status Value
Path Meaning
Fabric Meaning
Operational Enabled The path is fully functional and ready to use. At least one path in the fabric is enabled.
Operational Disabled The path is unable to provide any service. All paths in the fabric are disabled.
Availability Degraded None At least one path in the fabric is disabled and at least one path in the fabric is enabled.
Usage Active The path is in use (current path). At least one path in the fabric is active.
Usage Idle The path is not being used. No paths in the fabric are active (all are idle).
 


Using ServerNet States View for Maintenance Operations

The ServerNet States view can be used to verify that all paths between nodes are enabled, including those paths that are not in use. By verifying that the unused paths will work when needed, and repairing those paths that are disabled, you can prevent a node from being removed from the cluster in the case where one path fails and the second path to the node is already disabled.

When a path sustains a failure and transitions from enabled to disabled, the ServerNet Manager presents a dialog box warning of the failure. The dialog appears regardless of the NonStop Cluster Management Suite (NCMS) application currently being displayed as long as the ServerNet Manager is running.

It is important to take corrective action when the alarm dialog box is displayed so the problem can be fixed before another path failure occurs. If a path failure does occur, the ServerNet States view can be used to:

  1. Determine what paths are currently being used in the cluster, and
  2. Switch those paths needing it so maintenance can be performed on the cables and ServerNet SAN switch associated with the failing path without interrupting operation of the cluster.

If a second path failure occurs before the first failure was repaired, the second failure may cause a node to be removed from the cluster, depending on where the failures have occurred. For example:

NOTE: When the ServerNet States view is used to change the path used by a node, the change does not have the same impact on the paths used throughout the cluster as when the node switches paths due to a path failure. When a path fails, the node detecting the failure switches all of its communications to the other path. However, when the ServerNet States view is used to force a given node to communicate with one or more other nodes over a new path, those new path(s) only apply to communications originating from that node. Communications originating from the other nodes do not switch paths as they do when a path failure occurs.

Viewing Path/Fabric State and Status

Path States

The operational and usage states for all paths for a given SPA are contained in two panes of the ServerNet States view: Associated with each of these two panes is a SPA choice box used to select the SPA for which the paths are viewed. The amount of vertical space allotted to each pane within the NCMS window can be adjusted by dragging the horizontal line between the panes up or down or by clicking on the arrowheads on the line.

The columns in both panes contain the same type of information as described in the following table.
 
Column Heading
Column Content
Column Description
Path [n, m] Path from SPA n to SPA m.
X State Enabled, Disabled Operational state of X path from SPA n to SPA m.
Y State Enabled, Disabled Operational state of Y path from SPA n to SPA m.
Preferred X, Y, None Preferred path from SPA n to SPA m.
Current X, Y Current path from SPA n to SPA m. The path shown (X or Y) has a usage state of active; the path not shown is idle.

Fabric States and Status

The states and status for the X and Y fabrics are contained in two boxes: X Network and Y Network.

The first line of each box has one of three values for the fabric operational state and availability status: Enabled, Degraded, or Disabled. The second line in each box shows the fabric usage state: Active or Idle.


Designating a Preferred Path

Preferred paths should be designated when the ServerNet SAN packet traffic needs to be split between the X and Y fabrics for some reason, such as optimizing node-to-node communications performance. The  preferred paths become the current paths when communications are forced to all preferred paths as described under Forcing Communications to Path/Fabric and when the ServerNet Agent is started during the cluster boot process.

NOTE: Only users with root permission can designate a preferred path.

Preferred paths are designated with choice boxes (available only to users with root permissions) under the Preferred column of the Paths From SPA N and Paths To SPA N panes. A choice box for a given preferred path appears when you click in the associated cell under the Preferred column. For either pane, designate a preferred path as follows:

  1. Select the SPA that you want to designate a preferred path for with the SPA choice box next to the chosen pane.
  2. Under the Preferred column of the chosen pane, click in the cell (row) for the desired path to display the choice box.
  3. Use the displayed choice box to set the preferred path.
  4. Repeat Steps 1 through 3 as needed to designate the preferred paths in both panes for all SPAs.

Forcing Communications to Path/Fabric

NOTE: Only users with root permission can force ServerNet SAN communications to a designated path or fabric.

ServerNet SAN communications are forced on a path basis to the X or Y network with choice boxes (available only to users with root permission) under the Current column of the Paths From SPA N and Paths To SPA N panes. A choice box for a given current path appears when you click in the associated cell under the Current column. For either pane, force communications to the selected path as follows:

  1. Select the SPA for which you want to designate a current path with the SPA choice box next to the chosen pane.
  2. Under the Current column of the chosen pane, click in the cell (row) for the desired path to display the choice box.
  3. Use the displayed choice box to set the current path.
  4. Repeat Steps 1 through 3 as needed to designate the current paths in both panes for all SPAs.
To force communications on a path to the preferred path, use the preceding steps to set the current path to match the preferred path setting.

ServerNet SAN communications are forced to the X fabric, Y fabric, or the previously designated preferred paths with the buttons (available only to users with root permission) under the Use Network heading.