The multipath-tools package automatically detects the following storage arrays:

In general, most other storage arrays should work. When storage arrays are automatically detected, the default settings for multipathing apply. If you want non-default settings, you must manually create and configure the /etc/multipath.conf file. The same applies for hardware that is not automatically detected. For information, see Section 16.6, “Creating or Modifying the /etc/multipath.conf File”.

Consider the following caveats:

Storage arrays from the following vendors have been tested with SUSE Linux Enterprise Server:

Most other vendor storage arrays should also work. Consult your vendor’s documentation for guidance. For a list of the default storage arrays recognized by the multipath-tools package, see Section 16.2.1, “Storage Arrays That Are Automatically Detected for Multipathing”.

Storage arrays that require special commands on failover from one path to the other or that require special nonstandard error handling might require more extensive support. Therefore, the Device Mapper Multipath service has hooks for hardware handlers. For example, one such handler for the EMC CLARiiON CX family of arrays is already provided.

Important: For More Information

Consult the hardware vendor’s documentation to determine if its hardware handler must be installed for Device Mapper Multipath.

The multipath -t command shows an internal table of storage arrays that require special handling with specific hardware handlers. The displayed list is not an exhaustive list of supported storage arrays. It lists only those arrays that require special handling and that the multipath-tools developers had access to during the tool development.

Important: Exceptions

Arrays with true active/active multipath support do not require special handling, so they are not listed for the multipath -t command.

A listing in the multipath -t table does not necessarily mean that SUSE Linux Enterprise Server was tested on that specific hardware. For a list of tested storage arrays, see Section 16.2.2, “Tested Storage Arrays for Multipathing Support”.

Perform the following disk management tasks before you attempt to configure multipathing for a physical or logical device that has multiple paths:

Volume managers such as LVM2 and Clustered LVM2 run on top of multipathing. You must configure multipathing for a device before you use LVM2 or cLVM2 to create segment managers and file systems on it. For information, see Section 16.12, “Using LVM2 on Multipath Devices”.

The Linux software RAID management software runs on top of multipathing. For each device that has multiple I/O paths and that you plan to use in a software RAID, you must configure the device for multipathing before you attempt to create the software RAID device. Automatic discovery of multipathed devices is not available. The software RAID is not aware of the multipathing management running underneath.

For information about setting up multipathing for existing software RAIDs, see Section 16.13, “Configuring Multipath I/O for an Existing Software RAID”.

High-availability solutions for clustering storage resources run on top of the multipathing service on each node. Ensure that the configuration settings in the /etc/multipath.conf file on each node are consistent across the cluster.

Ensure that multipath devices have the same name across all devices. Refer to Section 16.9.1, “Multipath Device Names in HA Clusters” for details.

The Distributed Replicated Block Device (DRBD) high-availability solution for mirroring devices across a LAN runs on top of multipathing. For each device that has multiple I/O paths and that you plan to use in a DRDB solution, you must configure the device for multipathing before you configure DRBD.

The Device Mapper Multipath (DM-MP) module provides the multipathing capability for Linux. DM-MPIO is the preferred solution for multipathing on SUSE Linux Enterprise Server. It is the only multipathing option shipped with the product that is completely supported by SUSE.

DM-MPIO features automatic configuration of the multipathing subsystem for a large variety of setups. Configurations of up to eight paths to each device are supported. Configurations are supported for active/passive (one path active, others passive) or active/active (all paths active with round-robin load balancing).

The DM-MPIO framework is extensible in two ways:

The user space component of DM-MPIO takes care of automatic path discovery and grouping, and automated path retesting, so that a previously failed path is automatically reinstated when it becomes healthy again. This minimizes the need for administrator attention in a production environment.

DM-MPIO protects against failures in the paths to the device, and not failures in the device itself. If one of the active paths is lost (for example, a network adapter breaks or a fiber-optic cable is removed), I/O is redirected to the remaining paths. If the configuration is active/passive, then the path fails over to one of the passive paths. If you are using the round-robin load-balancing configuration, the traffic is balanced across the remaining healthy paths. If all active paths fail, inactive secondary paths must be woken up, so failover occurs with a delay of approximately 30 seconds.

If a disk array has more than one storage processor, ensure that the SAN switch has a connection to the storage processor that owns the LUNs you want to access. On most disk arrays, all LUNs belong to both storage processors, so both connections are active.

Note: Storage Processors

On some disk arrays, the storage array manages the traffic through storage processors so that it presents only one storage processor at a time. One processor is active and the other one is passive until there is a failure. If you are connected to the wrong storage processor (the one with the passive path) you might not see the expected LUNs, or you might see the LUNs but get errors when you try to access them.

Device Mapper Multipath detects every path for a multipathed device as a separate SCSI device. The SCSI device names take the form /dev/sdN, where N is an autogenerated letter for the device, beginning with a and issued sequentially as the devices are created, such as /dev/sda, /dev/sdb, and so on. If the number of devices exceeds 26, the letters are duplicated so that the next device after /dev/sdz will be named /dev/sdaa, /dev/sdab, and so on.

If multiple paths are not automatically detected, you can configure them manually in the /etc/multipath.conf file. The multipath.conf file does not exist until you create and configure it. For information, see Section 16.6, “Creating or Modifying the /etc/multipath.conf File”.

The packages multipath-tools and kpartx provide tools that take care of automatic path discovery and grouping. They automatically test the path periodically, so that a previously failed path is automatically reinstated when it becomes healthy again. This minimizes the need for administrator attention in a production environment.

Udev is the default device handler, and devices are automatically known to the system by the Worldwide ID instead of by the device node name. This resolves problems in previous releases of MDADM and LVM where the configuration files (mdadm.conf and lvm.conf) did not properly recognize multipathed devices.

As with LVM2, MDADM requires that the devices be accessed by the ID rather than by the device node path. Therefore, the DEVICE entry in /etc/mdadm.conf should be set as follows:

DEVICE /dev/disk/by-id/*

If you are using user-friendly names, specify the path as follows so that only the device mapper names are scanned after multipathing is configured:

DEVICE /dev/disk/by-id/dm-uuid-.*-mpath-.*

Use the Linux multipath(8) command to configure and manage multipathed devices. The general syntax for the command looks like the following:

multipath [-v verbosity_level] [-b bindings_file] [-d] [-h|-l|-ll|-f|-F|-B|-c|-q|-r|-w|-W] [-p failover|multibus|group_by_serial|group_by_prio|group_by_node_name] [devicename]

Refer to man 8 multipath for details.

The mpathpersist utility can be used to manage SCSI persistent reservations on Device Mapper Multipath devices. The general syntax for the command looks like the following:

mpathpersist [options] [device]

Refer to man 8 mpathpersist for details.

Use this utility with the service action reservation key (reservation_key attribute) in the /etc/multipath.conf file to set persistent reservations for SCSI devices. The attribute is not used by default. If it is not set, the multipathd daemon does not check for persistent reservation for newly discovered paths or reinstated paths.

reservation_key <reservation key>

You can add the attribute to the defaults section or the multipaths section. For example:

multipaths {
  multipath {
    wwid   XXXXXXXXXXXXXXXX
    alias      yellow
    reservation_key  0x123abc
  }
}

Set the reservation_key parameter for all mpath devices applicable for persistent management, then restart the multipathd daemon by running the following command:

sudo systemctl restart multipathd

After it is set up, you can specify the reservation key in the mpathpersist commands.

To enable multipath services to start at boot time, run the following command:

sudo systemctl enable multipathd

To manually start the service in the running system or to check its status, enter one of the following commands:

sudo systemctl start multipathd
sudo systemctl status multipathd

To stop the multipath services in the current session and to disable it, so it will not be started next time the system is booted, run the following commands:

sudo systemctl stop multipathd
sudo systemctl disable multipathd

Important: Rebuilding the initrd is Required

Whenever you enable or disable the multipath services it is also required to rebuild the initrd, otherwise the system may not boot anymore. When enabling the multipath services, proceed as descibed in Section 16.5.4, “Configuring the Device Drivers in initrd for Multipathing”.

If disabling the services, then revert the multipath related changes previously made to the force_drivers line in /etc/dracut.conf.d/01-dist.conf. Rebuild the initrd as described in the section mentioned above. Additionally and optionally, if you also want to make sure multipath devices do not get set up when starting multipath manually, add the following lines to the end of /etc/multipath.conf before rebuilding the initrd:

blacklist {
    wwid ".*"
}

Before configuring multipath I/O for your SAN devices, prepare the SAN devices, as necessary, by doing the following:

If the LUNs are not seen by the HBA driver, lsscsi can be used to check whether the SCSI devices are seen correctly by the operating system. When the LUNs are not seen by the HBA driver, check the zoning setup of the SAN. In particular, check whether LUN masking is active and whether the LUNs are correctly assigned to the server.

If the LUNs are seen by the HBA driver, but there are no corresponding block devices, additional kernel parameters are needed to change the SCSI device scanning behavior, such as to indicate that LUNs are not numbered consecutively. For information, see TID 3955167: Troubleshooting SCSI (LUN) Scanning Issues in the SUSE Knowledgebase at https://www.suse.com/support/kb/doc.php?id=3955167.

Partitioning devices that have multiple paths is not recommended, but it is supported. You can use the kpartx tool to create partitions on multipath devices without rebooting. You can also partition the device before you attempt to configure multipathing by using the Partitioner function in YaST, or by using a third-party partitioning tool.

Multipath devices are device-mapper devices. Modifying device-mapper devices with command line tools (such as parted, kpartx, or fdisk) works, but it does not necessarily generate the udev events that are required to update other layers. After you partition the device-mapper device, you should check the multipath map to make sure the device-mapper devices were mapped. If they are missing, you can remap the multipath devices or reboot the server to pick up all of the new partitions in the multipath map.

The device-mapper device for a partition on a multipath device is not the same as an independent device. When you create an LVM logical volume using the whole device, you must specify a device that contains no partitions. If you specify a multipath partition as the target device for the LVM logical volume, LVM recognizes that the underlying physical device is partitioned and the create fails. If you need to subdivide a SAN device, you can carve LUNs on the SAN device and present each LUN as a separate multipath device to the server.

The server must be manually configured to automatically load the device drivers for the controllers to which the multipath I/O devices are connected within the initrd. You need to add the necessary driver module to the variable force_drivers in the file /etc/dracut.conf.d/01-dist.conf.

For example, if your system contains a RAID controller accessed by the hpsa driver and multipathed devices connected to a QLogic controller accessed by the driver qla23xx, this entry would look like:

force_drivers+="hpsa qla23xx"

After changing /etc/dracut.conf.d/01-dist.conf, you must re-create the initrd on your system with the dracut -f command, then reboot for the changes to take effect.

There are four SCSI hardware handlers available in the SCSI layer that can be used with DM-Multipath:

Add the modules to the initrd image, then specify them in the /etc/multipath.conf file as hardware handler types alua, rdac, hp_sw, and emc. For example, add one of these lines for a device definition:

hardware_handler "1 alua"
hardware_handler "1 rdac"
hardware_handler "1 hp_sw"
hardware_handler "1 emc"

To include the modules in the initrd image:

The /etc/multipath.conf file is organized into the following sections. See man 5 multipath.conf for details.

Whenever you create or modify the /etc/multipath.conf file, the changes are not automatically applied when you save the file. You can perform a “dry run” of the setup to verify the multipath setup before you update the multipath maps.

At the server command prompt, enter

sudo multipath -v2 -d

This command scans the devices, then displays what the setup would look like if you commit the changes. It is assumed that the multipathd daemon is already running with the old (or default) multipath settings when you modify the /etc/multipath.conf file and perform the dry run. If the changes are acceptable, continue with the next step.

The output is similar to the following:

26353900f02796769
[size=127 GB]
[features="0"]
[hwhandler="1    emc"]

\_ round-robin 0 [first]
  \_ 1:0:1:2 sdav 66:240  [ready ]
  \_ 0:0:1:2 sdr  65:16   [ready ]

\_ round-robin 0
  \_ 1:0:0:2 sdag 66:0    [ready ]
  \_ 0:0:0:2 sdc   8:32   [ready ]

Paths are grouped into priority groups. Only one priority group is in active use at a time. To model an active/active configuration, all paths end in the same group. To model an active/passive configuration, the paths that should not be active in parallel are placed in several distinct priority groups. This normally happens automatically on device discovery.

The output shows the order, the scheduling policy used to balance I/O within the group, and the paths for each priority group. For each path, its physical address (host:bus:target:lun), device node name, major:minor number, and state is shown.

By using a verbosity level of -v3 in the dry run, you can see all detected paths, multipaths, and device maps. Both WWID and device node blacklisted devices are displayed.

The following is an example of -v3 output on a 64-bit SLES 11 SP2 server with two Qlogic HBAs connected to a Xiotech Magnitude 3000 SAN. Some multiple entries have been omitted to shorten the example.

tux > sudo multipath -v3 d
dm-22: device node name blacklisted
< content omitted >
loop7: device node name blacklisted
< content omitted >
md0: device node name blacklisted
< content omitted >
dm-0: device node name blacklisted
sdf: not found in pathvec
sdf: mask = 0x1f
sdf: dev_t = 8:80
sdf: size = 105005056
sdf: subsystem = scsi
sdf: vendor = XIOtech
sdf: product = Magnitude 3D
sdf: rev = 3.00
sdf: h:b:t:l = 1:0:0:2
sdf: tgt_node_name = 0x202100d0b2028da
sdf: serial = 000028DA0014
sdf: getuid= "/lib/udev/scsi_id --whitelisted --device=/dev/%n" (config file default)
sdf: uid = 200d0b2da28001400 (callout)
sdf: prio = const (config file default)
sdf: const prio = 1
[...]
ram15: device node name blacklisted
[...]
===== paths list =====
uuid              hcil    dev dev_t pri dm_st  chk_st  vend/prod/rev
200d0b2da28001400 1:0:0:2 sdf 8:80  1   [undef][undef] XIOtech,Magnitude 3D
200d0b2da28005400 1:0:0:1 sde 8:64  1   [undef][undef] XIOtech,Magnitude 3D
200d0b2da28004d00 1:0:0:0 sdd 8:48  1   [undef][undef] XIOtech,Magnitude 3D
200d0b2da28001400 0:0:0:2 sdc 8:32  1   [undef][undef] XIOtech,Magnitude 3D
200d0b2da28005400 0:0:0:1 sdb 8:16  1   [undef][undef] XIOtech,Magnitude 3D
200d0b2da28004d00 0:0:0:0 sda 8:0   1   [undef][undef] XIOtech,Magnitude 3D
params = 0 0 2 1 round-robin 0 1 1 8:80 1000 round-robin 0 1 1 8:32 1000
status = 2 0 0 0 2 1 A 0 1 0 8:80 A 0 E 0 1 0 8:32 A 0
sdf: mask = 0x4
sdf: path checker = directio (config file default)
directio: starting new request
directio: async io getevents returns 1 (errno=Success)
directio: io finished 4096/0
sdf: state = 2
[...]

Changes to the /etc/multipath.conf file cannot take effect when multipathd is running. After you make changes, save and close the file, then do the following to apply the changes and update the multipath maps:

Ensure that multipath devices have the same name across all devices by doing the following:

Note: User-Friendly Names

If you really need to use user-friendly names, you can force the system-defined user-friendly names to be consistent across all nodes in the cluster by doing the following:

1. In the /etc/multipath.conf file on one node:

   1. Set the user_friendly_names configuration option to yes to enable it.

      Multipath uses the /var/lib/multipath/bindings file to assign a persistent and unique name to the device in the form of mpath<n> in the /dev/mapper directory.

   2. (Optional) Set the bindings_file option in the defaults section of the /etc/multipath.conf file to specify an alternate location for the bindings file.

      The default location is /var/lib/multipath/bindings.

2. Set up all of the multipath devices on the node.

3. Copy the /etc/multipath.conf file from the node to the /etc/ directory of all the other nodes in the cluster.

4. Copy the bindings file from the node to the bindings_file path on all of the other nodes in the cluster.

Use the multipath command with the -p option to set the path failover policy:

sudo multipath devicename -p policy

Replace policy with one of the following policy options:

You must manually enter the failover priorities for the device in the /etc/multipath.conf file. Examples for all settings and options can be found in the /usr/share/doc/packages/multipath-tools/multipath.conf.annotated file.

Use the SCSI Report Target Port Groups (sg_rtpg(8)) command. For information, see the man page for sg_rtpg(8).

The multipath software must be running at install time if you want to install the operating system on a multipath device. The multipathd daemon is not automatically active during the system installation. You can start it by using the Configure Multipath option in the YaST Partitioner.

Add multipath=off to the kernel command line. This can be done with the YaST Boot Loader module. Open Boot Loader Installation › Kernel Parameters and add the parameter to both command lines.

This affects only the root device. All other devices are not affected.

By default, LVM2 does not recognize multipathed devices. To make LVM2 recognize the multipathed devices as possible physical volumes, you must modify /etc/lvm/lvm.conf to scan multipathed devices through the multipath I/O layer.

Adding a multipath filter prevents LVM from scanning and using the physical paths for raw device nodes that represent individual paths to the SAN (/dev/sd*). Ensure that you specify the filter path so that LVM scans only the device mapper names for the device (/dev/disk/by-id/dm-uuid-.*-mpath-.*) after multipathing is configured.

To modify /etc/lvm/lvm.conf for multipath use:

If your system has already been configured for multipathing and you later need to add more storage to the SAN, you can use the rescan-scsi-bus.sh script to scan for the new devices. By default, this script scans all HBAs with typical LUN ranges. The general syntax for the command looks like the following:

rescan-scsi-bus.sh [options] [host [host ...]]

For most storage subsystems, the script can be run successfully without options. However, some special cases might need to use one or more options. Run rescan-scsi-bus.sh --help for details.

Warning: EMC PowerPath Environments

In EMC PowerPath environments, do not use the rescan-scsi-bus.sh utility provided with the operating system or the HBA vendor scripts for scanning the SCSI buses. To avoid potential file system corruption, EMC requires that you follow the procedure provided in the vendor documentation for EMC PowerPath for Linux.

Use the following procedure to scan the devices and make them available to multipathing without rebooting the system.

Use the example in this section to detect a newly added multipathed LUN without rebooting.

Warning: EMC PowerPath Environments

In EMC PowerPath environments, do not use the rescan-scsi-bus.sh utility provided with the operating system or the HBA vendor scripts for scanning the SCSI buses. To avoid potential file system corruption, EMC requires that you follow the procedure provided in the vendor documentation for EMC PowerPath for Linux.

Querying the multipath I/O status outputs the current status of the multipath maps.

The multipath -l option displays the current path status as of the last time that the path checker was run. It does not run the path checker.

The multipath -ll option runs the path checker, updates the path information, then displays the current status information. This command always displays the latest information about the path status.

tux > sudo multipath -ll
3600601607cf30e00184589a37a31d911
[size=127 GB][features="0"][hwhandler="1 emc"]

\_ round-robin 0 [active][first]
  \_ 1:0:1:2 sdav 66:240  [ready ][active]
  \_ 0:0:1:2 sdr  65:16   [ready ][active]

\_ round-robin 0 [enabled]
  \_ 1:0:0:2 sdag 66:0    [ready ][active]
  \_ 0:0:0:2 sdc  8:32    [ready ][active]

For each device, it shows the device’s ID, size, features, and hardware handlers.

Paths to the device are automatically grouped into priority groups on device discovery. Only one priority group is active at a time. For an active/active configuration, all paths are in the same group. For an active/passive configuration, the passive paths are placed in separate priority groups.

The following information is displayed for each group:

The following information is displayed for each path:

You might need to configure multipathing to queue I/O if all paths fail concurrently by enabling queue_if_no_path. Otherwise, I/O fails immediately if all paths are gone. In certain scenarios, where the driver, the HBA, or the fabric experience spurious errors, DM-MPIO should be configured to queue all I/O where those errors lead to a loss of all paths, and never propagate errors upward.

When you use multipathed devices in a cluster, you might choose to disable queue_if_no_path. This automatically fails the path instead of queuing the I/O, and escalates the I/O error to cause a failover of the cluster resources.

Because enabling queue_if_no_path leads to I/O being queued indefinitely unless a path is reinstated, ensure that multipathd is running and works for your scenario. Otherwise, I/O might be stalled indefinitely on the affected multipathed device until reboot or until you manually return to failover instead of queuing.

To test the scenario:

To set up queuing I/O for scenarios where all paths fail:

If all paths fail concurrently and I/O is queued and stalled, do the following:

Testing of the IBM z Systems device with multipathing has shown that the dev_loss_tmo parameter should be set to 90 seconds, and the fast_io_fail_tmo parameter should be set to 5 seconds. If you are using z Systems devices, modify the /etc/multipath.conf file to specify the values as follows:

defaults {
       dev_loss_tmo 90
       fast_io_fail_tmo 5
}

The dev_loss_tmo parameter sets the number of seconds to wait before marking a multipath link as bad. When the path fails, any current I/O on that failed path fails. The default value varies according to the device driver being used. The valid range of values is 0 to 600 seconds. To use the driver’s internal timeouts, set the value to zero (0) or to any value greater than 600.

The fast_io_fail_tmo parameter sets the length of time to wait before failing I/O when a link problem is detected. I/O that reaches the driver fails. If I/O is in a blocked queue, the I/O does not fail until the dev_loss_tmo time elapses and the queue is unblocked.

If you modify the /etc/multipath.conf file, the changes are not applied until you update the multipath maps, or until the multipathd daemon is restarted (systemctl restart multipathd).

When using multipath for NetApp devices, we recommend the following settings in the /etc/multipath.conf file:

The --noflush option should always be used when running on multipath devices.

For example, in scripts where you perform a table reload, you use the --noflush option on resume to ensure that any outstanding I/O is not flushed, because you need the multipath topology information.

load
resume --noflush

A system with root (/) on a multipath device might stall when all paths have failed and are removed from the system because a dev_loss_tmo timeout is received from the storage subsystem (such as Fibre Channel storage arrays).

If the system device is configured with multiple paths and the multipath no_path_retry setting is active, you should modify the storage subsystem’s dev_loss_tmo setting accordingly to ensure that no devices are removed during an all-paths-down scenario. We strongly recommend that you set the dev_loss_tmo value to be equal to or higher than the no_path_retry setting from multipath.

The recommended setting for the storage subsystem’s dev_los_tmo is

<dev_loss_tmo> = <no_path_retry> * <polling_interval>

where the following definitions apply for the multipath values:

Each of these multipath values should be set from the /etc/multipath.conf configuration file. For information, see Section 16.6, “Creating or Modifying the /etc/multipath.conf File”.

During boot the system exits into the emergency shell with messages similar to the following:

[  OK  ] Listening on multipathd control socket.
         Starting Device-Mapper Multipath Device Controller...
[  OK  ] Listening on Device-mapper event daemon FIFOs.
         Starting Device-mapper event daemon...
         Expecting device dev-disk-by\x2duuid-34be48b2\x2dc21...32dd9.device...
         Expecting device dev-sda2.device...
[  OK  ] Listening on udev Kernel Socket.
[  OK  ] Listening on udev Control Socket.
         Starting udev Coldplug all Devices...
         Expecting device dev-disk-by\x2duuid-1172afe0\x2d63c...5d0a7.device...
         Expecting device dev-disk-by\x2duuid-c4a3d1de\x2d4dc...ef77d.device...
[  OK  ] Started Create list of required static device nodes ...current kernel.
         Starting Create static device nodes in /dev...
[  OK  ] Started Collect Read-Ahead Data.
[  OK  ] Started Device-mapper event daemon.
[  OK  ] Started udev Coldplug all Devices.
         Starting udev Wait for Complete Device Initialization...
[  OK  ] Started Replay Read-Ahead Data.
         Starting Load Kernel Modules...
         Starting Remount Root and Kernel File Systems...
[  OK  ] Started Create static devices
[   13.682489] floppy0: no floppy controllers found
[*     ] (1 of 4) A start job is running for dev-disk-by\x2du...(7s / 1min 30s)
[*     ] (1 of 4) A start job is running for dev-disk-by\x2du...(7s / 1min 30s)

...

Timed out waiting for device dev-disk-by\x2duuid-c4a...cfef77d.device.
[DEPEND] Dependency failed for /opt.
[DEPEND] Dependency failed for Local File Systems.
[DEPEND] Dependency failed for Postfix Mail Transport Agent.
Welcome to emergency shell
Give root password for maintenance
(or press Control-D to continue):

This issue is a logical consequence of the multipath integration in systemd and occurs if the root file system is not on multipath but multipath is enabled. In such a setup, multipath tries to set its paths for all devices that are not blacklisted. Since the device with the root file system is already mounted, it is inaccessible for multipath and causes it to fail.

Fix this issue by configuring multipath correctly by blacklisting the root device in /etc/multipath.conf:

Multipath must be loaded before LVM to ensure that multipath maps are built correctly. Loading multipath after LVM can result in incomplete device maps for a multipath device because LVM locks the device, and MPIO cannot create the maps properly.

If the system device is a local device that does not use MPIO and LVM, you can disable both boot.multipath and boot.lvm. After the server starts, you can manually start multipath before you start LVM, then run a pvscan command to recognize the LVM objects.

Timing is important for starting the LVM process. If LVM starts before MPIO maps are done, LVM might use a fixed path for the device instead of its multipath. The device works, so you might not be aware that the device’s MPIO map is incomplete until that fixed path fails. You can help prevent the problem by enabling boot.multipath and following the instructions in Section 16.15.2, “Enabling boot.multipath”.

To troubleshoot a mapping problem, you can use dmsetup to check that the expected number of paths are present for each multipath device. As the root user, enter the following at a command prompt:

sudo dmsetup ls --tree

In the following sample response, the first device has four paths. The second device is a local device with a single path. The third device has two paths. The distinction between active and passive paths is not reported through this tool.

tux > sudo dmsetup ls --tree
  vg910-lv00 (253:23)
    └─ 360a980006465576657346d4b6c593362 (253:10)
      |- (65:96)
      |- (8:128)
      |- (8:240)
      └─ (8:16)
  vg00-lv08 (253:9)
    └─ (8:3)
  system_vg-data_lv (253:1)
    └─36006016088d014007e0d0d2213ecdf11 (253:0)
      ├─ (8:32)
      └─ (8:48)

An incorrect mapping typically returns too few paths and does not have a major number of 253. For example, the following shows what an incorrect mapping looks like for the third device:

  system_vg-data_lv (8:31)
     └─ (8:32)

Multipath Tools from version 0.4.9 onward uses the prio setting in the defaults{} or devices{} section of the /etc/multipath.conf file. It silently ignores the keyword prio when it is specified for an individual multipath definition in the multipaths{) section.

Multipath Tools 0.4.8 allowed the prio setting in the individual multipath definition in the multipaths{) section to override the prio settings in the defaults{} or devices{} section.

When you upgrade from multipath-tools-0.4.8 to multipath-tools-0.4.9, the prio settings in the /etc/multipath.conf file are broken for prioritizers that require an argument. In multipath-tools-0.4.9, the prio keyword is used to specify the prioritizer, and the prio_args keyword is used to specify the argument for prioritizers that require an argument. Previously, both the prioritizer and its argument were specified on the same prio line.

For example, in multipath-tools-0.4.8, the following line was used to specify a prioritizer and its arguments on the same line.

prio "weightedpath hbtl [1,3]:.:.+:.+ 260 [0,2]:.:.+:.+ 20"

After upgrading to multipath-tools-0.4.9 or later, the command causes an error. The message is similar to the following:

<Month day hh:mm:ss> | Prioritizer 'weightedpath hbtl [1,3]:.:.+:.+ 260
[0,2]:.:.+:.+ 20' not found in /lib64/multipath

To resolve this problem, use a text editor to modify the prio line in the /etc/multipath.conf file. Create two lines with the prioritizer specified on the prio line, and the prioritizer argument specified on the prio_args line below it:

prio "weightedpath"
prio_args "hbtl [1,3]:.:.+:.+ 260 [0,2]:.:.+:.+ 20"

Restart the multipathd daemon for the changes to become active by running sudo systemctl restart multipathd.

For information about troubleshooting multipath I/O issues on SUSE Linux Enterprise Server, see the following Technical Information Documents (TIDs) in the SUSE Knowledgebase: