Red Hat Summit Red Hat SummitSupportKonsoleEntwicklerDemo startenKontakt

Dieser Inhalt ist in der von Ihnen ausgewählten Sprache nicht verfügbar.

Chapter 6. Managing multipathed volumes

You can manage multipath volumes by using the multipath, dmsetup, and multipathd commands, which are provided by Device Mapper (DM) Multipath to resize devices, move file systems, and administer the multipathd daemon.

6.1. Resizing an online multipath device
Link kopieren

Resize an online multipath device and its filesystem by using the multipathd and resize2fs commands. This allows you to expand storage capacity without downtime, ensuring applications remain available while scaling to meet growing data needs.

Procedure

  1. Resize your physical device.

  2. Find the paths to the logical unit number (LUN): 

    # multipath -l

  3. Resize your paths. For Small Computer System Interface (SCSI) devices, writing a 1 to the rescan file for the device causes the SCSI driver to rescan, as in the following command: 

    # echo 1 > /sys/block/path_device/device/rescan

    Ensure that you run this command for each of the path devices. For example, if your path devices are sda, sdb, sde, and sdf, run the following commands: 

    # echo 1 > /sys/block/sda/device/rescan
     
    # echo 1 > /sys/block/sdb/device/rescan
     
    # echo 1 > /sys/block/sde/device/rescan
     
    # echo 1 > /sys/block/sdf/device/rescan

  4. Resize your multipath device: 

    # multipathd resize map multipath_device

  5. Resize the file system, assuming no LVM or DOS partitions are used: 

    # resize2fs /dev/mapper/mpatha

Move the root filesystem from a single-path device to a multipath setup to ensure path redundancy for critical system data. This enhances reliability by allowing the system to boot and operate even if one storage path fails, improving overall availability.

Prerequisites

  • You have installed the device-mapper-multipath package.

Procedure

  1. Create the /etc/multipath.conf configuration file: 

    # mpathconf --enable

  2. Enable the multipathd service: 

    # systemctl enable multipathd.service
  3. If find_multipaths is not set to on, edit the blacklist and blacklist_exceptions sections of /etc/multipath.conf, as described in Preventing devices from multipathing.

  4. Add the WWID of the device to the /etc/multipath/wwids file: 

    # multipath -a /dev/sdb
     
    wwid '3600d02300069c9ce09d41c4ac9c53200' added

    Replace /dev/sdb with the root device name.

  5. Confirm that your configuration file is set up correctly: 

    # multipath -d 3600d02300069c9ce09d41c4ac9c53200
     
    : mpatha (3600d02300069c9ce09d41c4ac9c53200) undef 3PARdata,VV
size=446M features='1 queue_if_no_path' hwhandler='1 alua' wp=undef
`-+- policy='service-time 0' prio=50 status=undef
  `- 5:0:0:0 sdb 8:16 undef ready running

    Replace 3600d02300069c9ce09d41c4ac9c53200 with the WWID of your swap device.

  6. Rebuild the initramfs file system with multipath: 

    # dracut --force --add multipath
  7. Shut the machine down.
  8. Boot the machine.
  9. Make the other paths visible to the machine.

Verification

  • Check if the multipath device is created by running the following command: 

    # multipath -l | grep 3600d02300069c9ce09d41c4ac9c53200
     
    mpatha (3600d02300069c9ce09d41c4ac9c53200) dm-0 3PARdata,VV

Move swap file system from single-path to multipath storage to ensure redundancy and prevent performance issues. If swap uses Logical Volume Manager (LVM), no special steps are needed. However, non-LVM swap devices might require editing /etc/fstab to use the correct multipath device name.

Procedure

  1. Create the /etc/multipath.conf configuration file: 

    # mpathconf --enable

  2. Enable the multipathd service: 

    # systemctl enable multipathd.service
  3. If the find_multipaths configuration parameter is not set to on, edit the blacklist and blacklist_exceptions sections of the /etc/multipath.conf file, as described in Preventing devices from multipathing.

  4. Add the WWID of the device to the /etc/multipath/wwids file: 

    # multipath -a /dev/sdb
     
    wwid '3600d02300069c9ce09d41c4ac9c53200' added

    Replace /dev/sdb with the swap device name.

  5. Confirm that your configuration file is set up correctly: 

    # multipath -d 3600d02300069c9ce09d41c4ac9c53200
     
    : mpatha (3600d02300069c9ce09d41c4ac9c53200) undef 3PARdata,VV
size=446M features='1 queue_if_no_path' hwhandler='1 alua' wp=undef
`-+- policy='service-time 0' prio=50 status=undef
  `- 5:0:0:0 sdb 8:16 undef ready running

    Replace 3600d02300069c9ce09d41c4ac9c53200 with the WWID of your swap device.

  6. Set up an alias for the swap device in the /etc/multipath.conf file: 

    multipaths {
    multipath {
        wwid WWID_of_swap_device
        alias swapdev
    }
}

  7. Edit the /etc/fstab file and replace the old device path to the root device with the multipath device.

    For example, if you had the following entry in the /etc/fstab file: 

    /dev/sdb2 swap                    swap    defaults        0 0

    Change the entry to the following: 

    /dev/mapper/swapdev swap          swap    defaults        0 0

  8. Rebuild the initramfs file system with multipath: 

    # dracut --force --add multipath
  9. Shut the machine down.
  10. Boot the machine.
  11. Make the other paths visible to the machine.

Verification

  • Verify if the swap device is on the multipath device: 

    # swapon -s
     
    Filename                Type          Size Used    Priority
/dev/dm-3               partition     4169724 0    -2

    The file name should match the multipath swap device. 

    # readlink -f /dev/mapper/swapdev
     
    /dev/dm-3

6.4. Determining device mapper entries for multipath devices
Link kopieren

Identify device mapper entries for configured multipath devices by using the multipathd command. This helps link multipath device names to their underlying device mapper entries, aiding in monitoring, troubleshooting, and system administration tasks for accurate device identification.

Procedure

  • Display all device mapper devices: 

    # multipathd show maps format "%n %d"
     
    name   sysfs
mpathd dm-4
mpathb dm-3
mpatha dm-2
mpathh dm-9

6.5. Administering the multipathd daemon
Link kopieren

Manage and interact with the multipathd daemon by using its commands. Administering multipathd is essential for monitoring path status, viewing device info, and controlling multipath behavior in real-time without needing service restarts or system reboots.

Procedure

  • View the default format for the output of the multipathd show maps command: 

    # multipathd show maps
     
    name sysfs uuid
mpathc dm-0 360a98000324669436c2b45666c567942

  • Some multipathd commands include a format option followed by a wildcard. Display a list of available wildcards with the following command: 

    # multipathd show wildcards
     
    multipath format wildcards:
%n  name
%w  uuid
%d  sysfs
...

  • Display the multipath devices that multipathd is monitoring. Use wildcards to specify the shown fields: 

    # multipathd show maps format "%n %w %d %s"
     
    name   uuid                              sysfs vend/prod/rev
mpathc 360a98000324669436c2b45666c567942 dm-0  NETAPP,LUN

  • Display the paths that multipathd is monitoring. Use wildcards to specify the shown fields: 

    # multipathd show paths format "%n %w %d %s"
     
    target WWNN        uuid                              dev vend/prod/rev
0x50001fe1500d2250 3600508b4001080520001e00011700000 sdb HP,HSV210

  • Display data in a raw format: 

    # multipathd show maps raw format "%n %w %d %s"
     
    mpathc 360a98000324669436c2b45666c567942 dm-0 NETAPP,LUN

    In raw format, no headers are printed and the fields are not padded to align the columns with the headers. This output can be more easily used for scripting.

Red Hat logoGithubredditYoutubeTwitter

Lernen

Testen, kaufen und verkaufen

Communitys

Über Red Hat Dokumentation

Wir helfen Red Hat Benutzern, mit unseren Produkten und Diensten innovativ zu sein und ihre Ziele zu erreichen – mit Inhalten, denen sie vertrauen können. Entdecken Sie unsere neuesten Updates.

Mehr Inklusion in Open Source

Red Hat hat sich verpflichtet, problematische Sprache in unserem Code, unserer Dokumentation und unseren Web-Eigenschaften zu ersetzen. Weitere Einzelheiten finden Sie in Red Hat Blog.

Über Red Hat

Wir liefern gehärtete Lösungen, die es Unternehmen leichter machen, plattform- und umgebungsübergreifend zu arbeiten, vom zentralen Rechenzentrum bis zum Netzwerkrand.

Theme

© 2026 Red HatNach oben