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:
-
Link - A full-duplex channel between two nodes in the ServerNet
SAN. NonStop Cluster node types are end nodes (computers) and router nodes
(ServerNet SAN switches).
-
Path - One or more links and intervening router nodes connecting
two end nodes. For example, the path from end node 1 to end node 2 in a
cluster of three or more computers includes the link from node 1 to a ServerNet
SAN switch and a link from the switch to node 2.
-
Fabric (or network) - The collection of links, router node(s), and
end node ServerNet SAN ports connecting the end nodes into a cluster. A
NonStop Cluster contains two independent and redundant fabrics (X and Y)
for fault tolerance. Each end node contains two ServerNet SAN ports; one
connected to the X fabric (port X) and one connected to the Y fabric (port
Y).
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:
- Determine what paths are currently being used in the cluster, and
- 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:
-
If a single node is unable to communicate over either its X or Y paths
(nonrecoverable errors on both paths), it will be removed from the cluster.
-
If one node has a failure on the X path and a second node has a failure
on the Y path, the two nodes can no longer communicate. Since each node
in a cluster must be able to communicate directly with all other nodes,
one of the two nodes will be removed from the cluster.
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:
-
Paths From SPA N (where N is the SPA number), which shows
state information for all paths from the selected SPA to all other SPAs
in the cluster.
-
Paths To SPA N, which shows state information for all paths to the
selected SPA from all other SPAs in the cluster.
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:
-
Select the SPA that you want to designate a preferred path for with the
SPA choice box next to the chosen pane.
-
Under the Preferred column of the chosen pane, click in the cell (row)
for the desired path to display the choice box.
-
Use the displayed choice box to set the preferred path.
-
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:
-
Select the SPA for which you want to designate a current path with the SPA
choice box next to the chosen pane.
-
Under the Current column of the chosen pane, click in the cell (row) for
the desired path to display the choice box.
-
Use the displayed choice box to set the current path.
-
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.
-
X button - Click here to force communications to all X paths in the cluster.
-
Y button - Click here to force communications to all Y paths in the cluster.
-
Preferred button - Click here to force communications to the designated
preferred paths in the cluster. If no preferred path is designated
for a given path, its current path (X or Y) is not changed when this button
is selected.