ServerNet Cluster Manual

SCF Commands for SNETMON and the ServerNet
Cluster Subsystem
ServerNet Cluster Manual—520575-003
8-20
STATUS SUBNET, DETAIL Command Example
(Partial Display)
About IPC Paths and Connections
All processors in a ServerNet cluster are connected over a pair of physical ServerNet X
and Y fabrics. The fabric at a processor is said to be up if the processor can
communicate over that fabric; otherwise it is considered down.
A path is a unidirectional ServerNet communication conduit between a pair of
processors over one ServerNet fabric. A path is defined as a source processor, a
fabric, and a destination processor, in that order. Each processor in the ServerNet
cluster has a pair of paths, X and Y, to every other processor in the cluster. The other
processor could be in the same system or in another system. The definition of a path
includes a sense of direction. Between two processors A and B, there are four paths:
•
Path X from A to B (maintained by processor A)
•
Path Y from A to B (maintained by processor A)
•
Path X from B to A (maintained by processor B)
•
Path Y from B to A (maintained by processor B)
A message system connection between two processors is a logical bi-directional
ServerNet communication conduit that contains the four paths mentioned above. The
message system connection between processors A and B can be up only if there is
direct ServerNet connectivity between the processors in both directions. That is, at
least one of the paths from A to B must be up, and at least one of the paths from B to A
must be up.
Paths between processors exist in various states for a number of reasons. For
example, processor A might have put its X path to processor B in a hard down state
due to a barrier timeout. However, processor B might not have put its X path to
processor A in a down state, because it has not received any errors on it.
Consequently, the state of a path from A to B is not the same as the state of the path
from B to A.
An internal path is a path between a pair of processors within the same system. An
external path is a path between a local and a remote processor.
Paths and fabrics in a ServerNet cluster can fail and can also be repaired. In response
to a path or fabric failure, see If Path State Problems Are Indicated on page 8-17.