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Verifying FC paths to LUNs

When you configure your host for FC, you should verify that the active paths are optimized paths.

About this task

You can verify the paths by mapping a LUN to the host on each storage system node, generating I/O to the LUN, and then checking the FC statistics on each node.

For ONTAP, you must run the sysstat command through the nodeshell. You can access the nodeshell by using the system node run command. For information about how to use the system node run command, see the man page.

Steps

  1. Map a LUN to the host on each node.
  2. On the consoles of each node, display the statistics: sysstat -b
  3. Generate I/O to the LUNs.
  4. Check the FC statistics on each storage system node to verify that the non-optimized paths have zero traffic. The sysstat command periodically writes a line of statistics to the console. Check the Partner columns; the values should remain close to zero, while the FCP columns should show data.
    Note: Some initiators send occasional traffic over passive paths, so you typically see some traffic on non-optimized paths even when the system is correctly configured.
  5. Press Ctrl-C to exit the sysstat command on each console.
    If the partner values remain close to zero, the traffic is flowing over the correct paths. If the Partner values are high, as in the following example, the paths are not configured correctly.

Example of high partner values

In this example, all FC traffic is flowing over non-optimized paths. Some columns from the output of the sysstat command are removed from the example to make it easier to read.

CPU     FCP    Partner  Total   FCP    kB/s   Partner   kB/s 
                                in     out    in        out 
 26%    1785       0    1785   67096     43      0       0 
 17%    1679       0    1679   62265     40      0       0 
 15%    1709       0    1709   64985     41      0       0 
 14%    1764       0    1764   66816     42      0       0 
 15%    1777       0    1777   67430     43      0       0 
 14%    1737       0    1737   65934     42      0       0 
 15%    1771       0    1771   66583     42      0       0 
  9%    1573       0    1573   43245  53662      0       0 
  4%    1149       0    1149     202 152276      0       0 
 13%    1143       0    1143      27 148661      0       0 
  4%    1083       0    1083      26 144865      0       0 
  4%    1081       0       0   1081      26      0       0