Linux Device Mapper Multipath Support

• The StorNext File System does not currently support disks managed through the Linux Device Mapper tools other than those which are managed through multipathd. Disk paths showing up under the /dev/mapper path that are not multipathd devices will not be usable by StorNext due to Device Mapper taking exclusive control of the disk devices. See the Linux dmsetup documentation for details.

  Device Mapper will release exclusive control of a disk device if all of the Device Mapper partition entries are removed. Some customers have successfully used Device Mapper devices by using dmsetup to remove the partition entries for a particular device before attempting to mount StorNext File Systems. See the Linux dmsetup documentation for details.

  Note: Device Mapper control on specific devices may need to be removed after each reboot or after a device is first presented to a system.

• Not all RAIDs work with the DM Multipath Driver. Check with your storage vendor for compatibility.
• For detailed instructions on installing and configuring the DM Multipath Driver, refer to the Red Hat, SUSE, Debian, or Ubuntu documentation provided with your version of Linux.
• For StorNext to use Linux Device Mapper Multipath devices, you must make two changes to the /etc/multipath.conf file.
  1. Set user_friendly_names to yes.

  2. Add the following entry to the multipath.conf blacklist section to prevent multipathd from managing the SNFS volume devices:

     devnode "cvfsctl*"

     In addition, the use of the alias attribute in a multipath subsection of the multipath.conf file is not currently supported for devices used by StorNext. Its use can lead to mount failures.

• Using the cvpaths file and udev rules configuration files is typically unnecessary with Linux Device-Mapper with StorNext.

• Current versions of the Linux DM Multipath driver assign a default value of 1000 for rr_min_io which is too high for most configurations having multiple active paths to storage. Using a smaller value such as 32 will typically result in significantly improved performance. Refer to the Red Hat, SUSE, Debian, or Ubuntu documentation provided with your version of Linux for details on how to apply this setting.

  Note: Experimentation may be required to determine the optimal value.

• (On SUSE Linux Systems) In order to use Linux Device Mapper Multipath with Stornext, /etc/multipath.conf must be used because SUSE Linux does not install a multipath.conf, and Novell recommends against using it. Although SUSE Linux does not install a multipath.conf file by default, an example file, located at:

  /usr/share/doc/packages/multipath-tools/ multipath.conf.synthetic

  can be copied to:

  /etc/multipath.conf

• (On Ubuntu Linux Systems) There is no multipath.conf file installed by default. However, an example file, located at:

  /usr/share/doc/multipath-tools/examples/multipath.conf.synthetic

  can be copied to:

  /etc/multipath.conf

• (On Debian Linux Systems) There is no multipath.conf file installed by default and no example file is provided. Therefore, the multipath.conf file must be hand-crafted. Refer to your Debian documentation for additional information.

• (On Red Hat Linux Systems) Red Hat does install a multipath.conf file. By default, Red Hat multipath.conf file blacklists all multipath-capable targets. This means the following must be commented out:

  blacklist { devnode "*"}

  Note: After installing and/or updating the /etc/multipath.conf file, multipath services must be restarted for changes to take effect. For details, refer the documentation for your version of Linux.

If you are using a third-party multipath driver, you may need to use a cvpaths file. The cvpaths file directs StorNext to the multipath devices for the entire lun.

By default, below are the devices StorNext uses:

• Linux

  /dev/sd*

• AIX

  /dev/rhdisk*

• Solaris

  /dev/rdsk*

For example, the EMC Powerpath driver creates devices named /dev/emcpower* on Linux. If you do not tell StorNext to use the /dev/emcpower* devices, it will instead use the /dev/sd* devices. In the example below, a cvpaths file must be created to specify the following:

Other third-party multipath devices may use other path names. If you run the cvlabel -l command, the output will show which devices are being used by StorNext.

For additional information on configuring the cvpaths file, refer to the cvpaths man page from the command line, or the cvpaths entry in the MAN Pages Reference Guide.