Getting and Using Network Performance Data (vxrlink stats)

The vxrlink stats command reports detailed information about the state of the network. It displays network statistics that can be used to assess network problems. Use the network performance data to determine the optimum network configuration for efficient use of system resources.

The vxrlink stats command can be executed repeatedly at given intervals using the -i interval option. In this case, the displayed values indicate the change since the last interval, except for the average round-trip value, which displays a moving average. The vxrlink stats command can be executed from the Primary and the Secondary. The RLINK statistics are reset when the RLINK disconnects. For detailed information on available options, refer to the vxrlink manual page.

The output of the vxrlink stats command includes the following details:

• Number of messages transmitted.
• Number of 1024-byte blocks transmitted
• Average round-trip per message.
  The size of the message affects the average round-trip per message.
• Number of timeouts or lost packets.
  If the number of timeouts is high, it indicates that network is very lossy. This needs to be fixed.
• Number of stream errors
  Stream errors occur when the RLINK attempts to send messages faster than the network can handle.
• Number of memory errors
  Memory errors occur when the secondary has insufficient buffer space to handle incoming messages. To reduce the number of errors, try increasing the value of the tunable, vol_max_nmpool_sz on the secondary.
• Current Timeout Value
  This represents the packet timeout in milliseconds.

Displaying Extended Replication Statistics

You can use the vxrlink stats command with the -e option to generate extended statistics, in addition to the statistics generated by the vxrlink stats command. The output generated by this command can be useful in assessing the reason for failure at the time it occurred.

The vxrlink stats -e command can be executed repeatedly at given intervals using the -i interval option. In this case, the displayed values indicate the change since the last interval. The vxrlink stats -e command can be executed from the Primary as well as the Secondary. The RLINK statistics are reset when the RLINK disconnects.

For detailed information about the available options, refer to the vxrlink manual page.

The output of the vxrlink stats -e command is displayed under the headings Messages and Errors. Each of these headings has the appropriate fields to display the required information. The first is the Messages heading which displays the following information:

• Number of blocks sent

Displays the number of1024 bytes that have been transmitted. This is different from the Blocks attribute displayed by the vxrlink stats command (without the -e option), which only displays the number of blocks that have been acknowledged.

The Messages heading is followed by the Errors heading. It has nine fields that display the different kinds of error encountered, three of which are similar to that in the
vxrlink stats command. The output includes the following details:

• No memory available

This error occurs when there is no space in the systems kernel memory to process the message.

• No message slots available

This error occurs if there is no memory to store the packets of the message that have arrived out of sequence. If a packet arrives out of sequence then it requires to be stored in the message buffer until all the related out-of-sequence packets arrive and can be assembled.

• No memory available in nmcom pool on Secondary

The buffer space determined by the VVR tunable vol_max_nmpool_sz is already full and cannot store any new messages that arrive at the Secondary.

• Timeout errors

Indicates the number of timeout errors, that is, the number of times the Primary timed out while waiting for an acknowledgement from the Secondary.

• Missing packet errors

Indicates the number of times the last packet of a message was received, before one or more packets of the same message were received.

• Missing message errors

Indicates the number of times messages have arrived out of sequence.

• Stream errors

Stream errors occur when the RLINK attempts to send messages faster than the network can handle.

• Checksum errors

Displays the number of data checksum errors. Every time a packet is received at the Secondary VVR performs a checksum to ensure that the packet data is the same as that sent by the Primary.

• Unable to deliver due to transaction errors

Displays the number of times the packets could not be delivered to the Secondary, due to transaction errors. If the Secondary is busy with some kernel operations when the packet arrives at the Secondary, then these packets may not be delivered until the transaction is complete.