OpenVMS Cluster Systems - OpenVMS Systems - HP

Troubleshooting the NISCA Protocol
F.2 Addressing LAN Communication Problems
Table F–3 (Cont.) System Parameters for Timing
Parameter Use
SHADOW_MBR_TIMEOUT
Defines the amount of time that the Volume
Shadowing for OpenVMS tries to recover from
a transient disk error on a single member of a
multiple-member shadow set.
SHADOW_MBR_TIMEOUT differs from
MVTIMEOUT because it removes a failing
shadow set member quickly. The remaining
shadow set members can recover more rapidly
once the failing member is removed.
Note: The TIMVCFAIL system parameter, which optimizes the amount of time
needed to detect a communication failure, is not recommended for use with
LAN communications. This parameter is intended for CI and DSSI connections.
PEDRIVER (which is for Ethernet and FDDI) usually surpasses the detection
provided by TIMVCFAIL with the listen timeout of 8 to 9 seconds.
F.2.7 Channel Timeouts
Channel timeouts are detected by PEDRIVER as described in Table F–4.
Table F–4 Channel Timeout Detection
PEDRIVER Actions Comments
Listens for HELLO datagram messages, which
are sent over channels at least once every 3
seconds
Closes a channel when HELLO datagrams or
sequenced messages have not been received for a
period of 8 to 9 seconds
Closes a virtual circuit when:
• No channels are available.
• The packet size of the only available
channels is insufficient.
Every node in the OpenVMS Cluster multicasts
HELLO datagram messages on each LAN
adapter to notify other nodes that it is still
functioning. Receiving nodes know that the
network connection is still good.
Because HELLO datagram messages are
transmitted at least once every 3 seconds,
PEDRIVER times out a channel only if at least
two HELLO datagram messages are lost and
there is no sequenced message traffic.
The virtual circuit is not closed if any other
channels to the node are available except
when the packet sizes of available channels
are smaller than the channel being used for
the virtual circuit. For example, if a channel
fails over from FDDI to Ethernet, PEDRIVER
may close the virtual circuit and then reopen it
after negotiating the smaller packet size that is
necessary for Ethernet segmentation.
Does not report errors when a channel is closed OPCOM ‘‘Connection loss’’ errors or SYSAP
messages are not sent to users or other system
applications until after the virtual circuit
shuts down. This fact is significant, especially
if there are multiple paths to a node and a
LAN hardware failure occurs. In this case, you
might not receive an error message; PEDRIVER
continues to use the virtual circuit over another
available channel.
Reestablishes a virtual circuit when a channel
becomes available again
F–8 Troubleshooting the NISCA Protocol
PEDRIVER reopens a channel when HELLO
datagram messages are received again.