Using a large number of LUNs and/or paths with MPIO

This document (7008051) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 11
SUSE Linux Enterprise Server 11 Service Pack 1

Situation

In environments with large numbers of LUNs and/or paths to those LUNs, multipathd may be unable to create the multipath maps for all the devices. When this occurs, the following message (or a similar message) is seen in /var/log/messages:

  multipathd:  error creating pipe for callout: Too many open files


Resolution

Multipathd requires open file descriptors for each managed path. In the startup script for multipathd (/etc/init.d/multipathd), the maximum number of open file descriptors is increased from the system default of 1024 to 4096. However, in environments with large numbers of LUNs and/or paths to those LUNs, this value may be insufficient.

As a general rule of thumb, there should be two available file descriptors per path. For example, if 1000 LUNs were available through 4 paths each, multipathd would need 8000 open file descriptors (#LUNs x #paths x 2).

To increase the maximum number of file descriptors, the following entry must be place in /etc/multipath.conf:

  defaults {
           max_fds   <VALUE>
          }

Note - It is very common for no /etc/multipath.conf file to exist. In this case, create the file using only the configuration option listed above. Otherwise, add the max_fds setting to the 'defaults' section of the existing multipath.conf file. If the server is booting from the SAN, run `mkinitrd` to ensure the new multipath.conf is added to the initrd.

After modifying (or creating) the /etc/multipath.conf file, restart multipathd to cause the setting to take effect.

Additional Information

Novell has tested multipathd with 16,000 available LUN/path combinations. As long as the system has enough resources to support the required open files, and the max_fds is set appropriately, large numbers of LUNs and/or paths should work properly.

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:7008051
  • Creation Date: 04-Mar-2011
  • Modified Date:03-Mar-2020
    • SUSE Linux Enterprise Server

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