Red Hat Summit Red Hat SummitSupportConsoleDevelopersStart a trialContact

Chapter 5. Preventing devices from multipathing

You can configure DM Multipath to ignore selected devices when it configures multipath devices. DM Multipath does not group these ignored devices into a multipath device.

DM Multipath uses the find_multipaths parameter and device discovery rules to automatically determine when to create multipath devices for detected storage paths.

DM Multipath has default rules to determine whether to create a multipath device for a path or ignore it. You can configure the behavior.

If find_multipaths is set to off, multipath always tries to create a multipath device for every non-disabled path. If the find_multipaths configuration parameter is set to on, then multipath creates a device, only if one of following conditions is met:

  • There are at least two paths with the same World-Wide Identification (WWID) that are not disabled.
  • You manually force the creation of the device by specifying a device with the multipath command.
  • A path has the same WWID as a previously created multipath device, even if that device no longer exists. Whenever a multipath device is created, multipath remembers its WWID. It then automatically recreates the device when it detects a path with that WWID. This lets multipath automatically choose the correct paths to make into multipath devices, without having to disable multipathing on other devices.

If you created a multipath device without using find_multipaths and later set it to on, remove unwanted device WWIDs from /etc/multipath/wwids. The following example shows a sample /etc/multipath/wwids file. The WWIDs are enclosed by slashes (/): 

# Multipath wwids, Version : 1.0
# NOTE: This file is automatically maintained by multipath and multipathd.
# You should not need to edit this file in normal circumstances.
#
# Valid WWIDs:
/3600d0230000000000e13955cc3757802/
/3600d0230000000000e13955cc3757801/
/3600d0230000000000e13955cc3757800/
/3600d02300069c9ce09d41c31f29d4c00/
/SWINSYS  SF2372         0E13955CC3757802/
/3600d0230000000000e13955cc3757803/

In addition to on and off, you can also set find_multipaths to the following values:

strict
Multipath never accepts paths that have not previously been multipathed and are therefore not in the /etc/multipath/wwids file.
smart
Multipath always accepts non-disabled devices in udev as soon as they appear. If multipathd does not create the device within the timeout set in the find_multipaths_timeout parameter, it releases its claim on the device.

The built-in default value of find_multipaths is off. The default multipath.conf file created by mpathconf, however, will set the value of find_multipaths to on.

When find_multipaths is set to on, disable multipathing only on devices with multiple paths that you do not want multipathed. Because of this, it will generally not be necessary to disable multipathing on devices.

If you add a multipath device to blacklist, remove its WWID from the /etc/multipath/wwids file by using the -w option. This avoids issues with other programs. For example, to remove the device /dev/sdb with WWID 3600d0230000000000e13954ed5f89300 from the /etc/multipath/wwids file, you can use either of the following methods.

  • Removing a multipath device by using the device name. 

    # multipath -w /dev/sdb
     
    wwid '3600d0230000000000e13954ed5f89300' removed

  • Removing a multipath device by using the WWID of the device. 

    # multipath -w 3600d0230000000000e13954ed5f89300
     
    wwid '3600d0230000000000e13954ed5f89300' removed

You can also use the -W option to update the /etc/multipath/wwids file. This would reset the /etc/multipath/wwids file to only include the WWIDs of the current multipath devices. To reset the file, run the following: 

# multipath -W
 
successfully reset wwids

Device exclusion from multipathing uses criteria such as, WWID, device name, type, property, or protocol, evaluated in priority order with exception lists taking precedence.

You can disable multipathing on devices by any of the following criteria:

  • WWID
  • device name
  • device type
  • property
  • protocol
Note

By default, a variety of device types are disabled, even after you comment out the initial blacklist section of the configuration file.

For every device, DM Multipath evaluates these criteria in the following order:

  1. property
  2. devnode
  3. device
  4. protocol
  5. wwid

If a device turns out to be disabled by any of the mentioned criteria, DM Multipath excludes it from handling by multipathd, and does not evaluate the later criteria. For each criteria, the exception list takes precedence over the list of disabled devices, if a device matches both.

5.3. Disabling multipathing by WWID
Copy link

Exclude specific devices from multipath by disabling them by using their WWID in the multipath.conf file. This is useful for local disks, single-path devices, or storage needing special handling outside the multipath framework.

Procedure

  1. Find WWID of a device: 

    # multipathd show paths raw format "%d %w" | grep sdb
     
    sdb 3600508b4001080520001e00011700000

  2. Disable devices in the /etc/multipath.conf configuration file by using the wwid entry.

    The following example shows the lines in the DM Multipath configuration file that disable a device with a WWID of 3600508b4001080520001e00011700000: 

    blacklist {
       wwid 3600508b4001080520001e00011700000
}

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null

    • To display the new configuration with the changes added, run: 

      # multipath -t

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload

5.4. Disabling multipathing by device name
Copy link

Disable multipathing for specific devices by using their device names, such as /dev/sda in the multipath.conf file. This prevents DM Multipath from grouping local disks, USB devices, or other storage into multipath devices, keeping them as individual block devices.

Procedure

  1. Display device information: 

    # udevadm info --query=all -n /dev/mapper/sd*

  2. Disable devices in the /etc/multipath.conf configuration file by using the devnode entry. The following example shows the lines in the DM Multipath configuration file that disable all SCSI devices, because it disables all sd* devices as well: 

    blacklist {
       devnode "^sd[a-z]"
}

    You can use a devnode entry to disable individual devices rather than all devices of a specific type. However, this is not recommended because unless it is statically mapped by udev rules, there is no guarantee that a specific device will have the same name on reboot. For example, a device name could change from /dev/sda to /dev/sdb on reboot.

    By default, DM Multipath disables all devices that are not the following:

    • Small Computer System Interface (SCSI)
    • Non-Volatile Memory Express (NVMe)

    • Direct Access Storage Device (DASD).

      To disable, it uses the following devnode entry: 

      blacklist {
       devnode "!^(sd[a-z]|dasd[a-z]|nvme[0-9])"
}

      The devices that this entry disables do not generally support DM Multipath.

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null

    • To display the new configuration with the changes added, run: 

      # multipath -t

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload

5.5. Disabling multipathing by device type
Copy link

Exclude entire categories of devices from multipath by specifying vendor and product info in the device section of multipath.conf. This prevents DM Multipath from grouping devices of certain models or vendors, keeping them as individual block devices.

Procedure

  1. Display device type: 

    # multipathd show paths raw format "%d %s" | grep sdb
     
    sdb HP,HSV210

  2. Disable devices in the /etc/multipath.conf configuration file by using the device section.

    The following example disables multipathing on all IBM DS4200 and HP devices: 

    blacklist {
       device {
               vendor  "IBM"
               product "3S42"       #DS4200 Product 10
       }
       device {
               vendor  "HP"
               product ".*"
       }
}

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null

    • To display the new configuration with the changes added, run: 

      # multipath -t

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload

5.6. Disabling multipathing by udev property
Copy link

Exclude devices from multipath by using their udev properties in the multipath.conf file. This method allows flexible filtering based on system-detected attributes like hardware type or connection, giving precise control over which devices are excluded from multipathing.

Procedure

  1. Display the udev variables for a device: 

    # udevadm info --query=all -n /dev/sdb

  2. Disable devices in the /etc/multipath.conf configuration file by using the property parameter. This parameter is a regular expression string that matches against the udev environment variable name for the devices.

    The following example disables multipathing on all devices with the udev property ID_ATA: 

    blacklist {
        property "ID_ATA"
}

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null

    • To display the new configuration with the changes added, run: 

      # multipath -t

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload

5.7. Disabling multipathing by device protocol
Copy link

Exclude devices from multipath based on their transport protocol by using the device protocol setting in multipath.conf. This is useful for preventing multipathing on local or specific protocols better managed outside the multipath framework.

Procedure

  1. Optional: View the protocol that a path is using: 

    # multipathd show paths raw format "%d %P" | grep sdb
     
    sdb scsi:fcp

  2. Disable devices in the /etc/multipath.conf configuration file by using the protocol parameter.

    The protocol parameter takes a regular expression and blacklists all devices with matching protocol strings. For example, to disable multipathing on all nvme devices, use the following: 

    blacklist {
        protocol "nvme"
}

    DM Multipath recognizes the protocol strings such as scsi:fcp, scsi:spi, scsi:ssa, scsi:sbp, scsi:srp, scsi:iscsi, scsi:sas, scsi:adt, scsi:ata, scsi:unspec, ccw, cciss, nvme:pcie, nvme:rdma, nvme:fc, nvme:tcp, nvme:loop, nvme:apple-nvme, nvme:unspec, and undef.

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null

    • To display the new configuration with the changes added, run: 

      # multipath -t

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload

Re-enable multipathing for specific devices by adding exceptions in multipath.conf. This is useful when broad exclusion rules are in place but certain devices still require multipathing. This allows precise control over which devices are managed by DM Multipath.

Prerequisites

  • Multipathing is disabled on certain devices.

Procedure

  1. Enable multipathing on the devices by using the blacklist_exceptions section of the /etc/multipath.conf configuration file.

    When specifying devices in the blacklist_exceptions section, you must use the same criteria as the blacklist section. For example, a WWID exception does not apply to devices disabled by a devnode entry, even if associated with that WWID. Similarly, devnode exceptions apply only to devnode entries, and device exceptions apply only to device entries.

    Following is an example for adding exceptions for devices with disabled multipathing

    • An exception by WWID

      If you have many devices and want to multipath only one with WWID 3600d0230000000000e13955cc3757803, you can disable all devices, then add an exception. Add the following lines to the /etc/multipath.conf file: 

      blacklist {
        wwid ".*"
}

blacklist_exceptions {
        wwid "3600d0230000000000e13955cc3757803"
}

      Alternatively, you can use an exclamation mark (!) to invert the blacklist entry, which disables all devices except the specified WWID: 

      blacklist {
        wwid "!3600d0230000000000e13955cc3757803"
}

    • An exception by udev property

      The property parameter works differently than the other blacklist_exception parameters. The value of the property parameter must match the name of a variable in the udev database. Otherwise, the device is disabled. Using this parameter, you can disable multipathing on certain SCSI devices, such as USB sticks and local hard drives.

      To enable multipathing only on SCSI devices that can reasonably be multipathed, set this parameter to (SCSI_IDENT_|ID_WWN) as in the following example: 

      blacklist_exceptions {
        property "(SCSI_IDENT_|ID_WWN)"
}

  2. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null

    • To display the new configuration with the changes added, run: 

      # multipath -t

  3. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
Red Hat logoGithubredditYoutubeTwitter

Learn

Try, buy, & sell

Communities

About Red Hat Documentation

We help Red Hat users innovate and achieve their goals with our products and services with content they can trust. Explore our recent updates.

Making open source more inclusive

Red Hat is committed to replacing problematic language in our code, documentation, and web properties. For more details, see the Red Hat Blog.

About Red Hat

We deliver hardened solutions that make it easier for enterprises to work across platforms and environments, from the core datacenter to the network edge.

Theme

© 2026 Red HatBack to top