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Chapter 5. DM-Multipath Administration and Troubleshooting

24

The following command sequence ensures that multipath has picked up any changes to the

multipath.conf

,

#

multipathd -k

> >

reconfigure

> >

CTRL-D

Use the following command sequence to ensure that the path checker is working properly.

#

multipathd -k

> >

show paths

> >

CTRL-D

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Summary of Contents for CLUSTER SUITE 4.7 DM MULTIPATH

Page 1: ...Red Hat Cluster Suite 4 7 DM Multipath DM Multipath Configuration and Administration ...

Page 2: ...the work or derivative of the work in any standard paper book form for commercial purposes is prohibited unless prior permission is obtained from the copyright holder Red Hat and the Red Hat Shadow Man logo are registered trademarks of Red Hat Inc in the United States and other countries All other trademarks referenced herein are the property of their respective owners The GPG fingerprint of the s...

Page 3: ...etting Up DM Multipath 7 3 2 Ignoring Local Disks when Generating Multipath Devices 8 3 3 Adding Devices to the Multipathing Database 10 4 The DM Multipath Configuration File 11 4 1 Configuration File Overview 11 4 2 Configuration File Blacklist 12 4 2 1 Blacklisting by WWID 12 4 2 2 Blacklisting By Device Name 12 4 3 Configuration File Defaults 13 4 4 Multipaths Device Configuration Attributes 15...

Page 4: ...iv ...

Page 5: ...lved in creating a secured computing environment for the data center workplace and home For more information about Red Hat Cluster Suite for Red Hat Enterprise Linux refer to the following resources Red Hat Cluster Suite Overview Provides a high level overview of the Red Hat Cluster Suite Configuring and Managing a Red Hat Cluster Provides information about installing configuring and managing Red ...

Page 6: ...ystem If not alternative but equivalent typefaces are displayed Note Red Hat Enterprise Linux 5 and later includes the Liberation Fonts set by default 4 1 Typographic Conventions Four typographic conventions are used to call attention to specific words and phrases These conventions and the circumstances they apply to are as follows Mono spaced Bold Used to highlight system input including shell co...

Page 7: ... the Text to copy field and then click the Copy button Now switch back to your document and choose Edit Paste from the gedit menu bar The above text includes application names system wide menu names and items application specific menu names and buttons and text found within a GUI interface all presented in Proportional Bold and all distinguishable by context Note the shorthand used to indicate tra...

Page 8: ...lti line data types are set off visually from the surrounding text Output sent to a terminal is set in Mono spaced Roman and presented thus books Desktop documentation drafts mss photos stuff svn books_tests Desktop1 downloads images notes scripts svgs Source code listings are also set in Mono spaced Roman but are presented and highlighted as follows package org jboss book jca ex1 import javax nam...

Page 9: ...at makes your life easier Important Important boxes detail things that are easily missed configuration changes that only apply to the current session or services that need restarting before an update will apply Ignoring Important boxes won t cause data loss but may cause irritation and frustration Warning A Warning should not be ignored Ignoring warnings will most likely cause data loss ...

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Page 11: ...h the cable switch or controller fails DM Multipath switches to an alternate path Improved Performance DM Multipath can be configured in active active mode where I O is spread over the paths in a round robin fashion In some configurations DM Multipath can detect loading on the I O paths and dynamically re balance the load Figure 1 1 Active Passive Multipath Configuration with One RAID Device shows...

Page 12: ...ultipath Configuration with Two RAID Devices As in the example shown in Figure 1 1 Active Passive Multipath Configuration with One RAID Device there are two I O paths to each RAID device With DM Multipath configured a failure at any of the points of the I O path to either of the RAID devices will cause DM Multipath to switch to the alternate I O path for that device Figure 1 3 Active Active Multip...

Page 13: ...ath Configuration File Some storage arrays require special handling of I O errors and path switching These require separate hardware handler kernel modules 1 3 DM Multipath Components Table 1 1 DM Multipath Components describes the components of DM Multipath Component Description dm multipath kernel module Reroutes I O and supports failover for paths and path groups multipath command Lists and con...

Page 14: ...default settings that are suitable for common multipath configurations Setting up DM multipath is often a simple procedure The basic procedure for configuring your system with DM Multipath is as follows 1 Install device mapper multipath rpm 2 Edit the multipath conf configuration file comment out the default blacklist change any of the existing defaults as needed save the configuration file 3 Star...

Page 15: ...ces to access the multipathed devices for example when creating logical volumes The devices in dev mpath are provided as a convenience so that all multipathed devices can be seen in one directory These devices are created by the udev device manager and may not be available on startup when the system needs to access them Do not use these devices for creating logical volumes or filesystems Any devic...

Page 16: ...onfiguration Attributes 2 4 Multipath Devices in Logical Volumes After creating multipath devices you can use the multipath device names just as you would use a physical device name when creating an LVM physical volume For example if dev mapper mpath0 is the name of a multipath device the following command will mark dev mapper mpath0 as a physical volume pvcreate dev mapper mpath0 You can use the ...

Page 17: ...ltipathing devnode_blacklist devnode After commenting out those lines this section appears as follows devnode_blacklist devnode 2 The default settings for DM Multipath are compiled in to the system and do not need to be explicitly set in the etc multipath conf file The default value of path_grouping_policy is set to failover so in this example you do not need to change the default value For inform...

Page 18: ...heir internal disks DM Multipath is not recommended for these devices The following procedure shows how to modify the multipath configuration file to ignore the local disks when configuring multipath 1 Determine which disks are the internal disks and mark them as the ones to blacklist In this example dev sda is the internal disk Note that as originally configured in the default multipath configura...

Page 19: ...be safe procedure since dev sda is not guaranteed to be the same on reboot To blacklist individual devices you can blacklist using the WWID of that device Note that in the output to the multipath vs command the WWID of the dev sda device is SIBM ESXSST336732LC____F3ET0EP0Q000072428BX1 To blacklist this device include the following in the etc multipath conf file devnode_blacklist wwid SIBM ESXSST33...

Page 20: ...path includes support for the most common storage arrays that support DM Multipath The default configuration values including supported devices can be found in the multipath conf defaults file If you need to add a storage device that is not supported by default as a known multipath device edit the etc multipath conf file and insert the appropriate device information For example to add information ...

Page 21: ...values specified in the multipath conf defaults file If there are sections of the file that are not relevant to your environment or for which you do not need to override the default values you can leave them commented out as they are in the initial file The configuration file allows regular expression description syntax An annotated version of the configuration file can be found in usr share doc d...

Page 22: ...acklist devices according to the following criteria By WWID as described in Section 4 2 1 Blacklisting by WWID By device name as described in Section 4 2 2 Blacklisting By Device Name By default a variety of device types are blacklisted even after you comment out the initial devnode_blacklist section of the configuration file For information see Section 4 2 2 Blacklisting By Device Name 4 2 1 Blac...

Page 23: ...generally support DM Multipath blacklist devnode ram raw loop fd md dm sr scd st 0 9 devnode hd a z devnode cciss c 0 9 d 0 9 4 3 Configuration File Defaults The etc multipath conf configuration file includes a defaults section that sets the user_friendly_names parameter to yes as follows defaults user_friendly_names yes This overwrites the default value of the user_friendly_names parameter The co...

Page 24: ...gorithm to use in determining what path to use for the next I O operation The default value is round robin 0 path_grouping_policy Specifies the default path grouping policy to apply to unspecified multipaths Possible values include failover 1 path per priority group multibus all valid paths in 1 priority group group_by_serial 1 priority group per detected serial number group_by_prio 1 priority gro...

Page 25: ...ic value for this attribute specifies the number of times the system should attempt to use a failed path before disabling queueing A value of fail indicates immediate failure without queuing A value of queue indicates that queuing should not stop until the path is fixed The default value is null user_friendly_names If set to yes specifies that the system should using the bindings file var lib mult...

Page 26: ...rr_weight If set to priorities then instead of sending rr_min_io requests to a path before calling selector to choose the next path the number of requests to send is determined by rr_min_io times the path s priority as determined by the prio_callout program Currently there are priority callouts only for devices that use the group_by_prio path grouping policy which means that all the paths in a pat...

Page 27: ...th conf defaults file You probably will not need to modify the values for these devices but if you do you can overwrite the default values by including an entry in the the configuration file for the device that overwrites those values You can copy the device configuration defaults from the multipath conf defaults file for the device and override the values that you want to change To add a device t...

Page 28: ...ly to unspecified multipaths Possible values include failover 1 path per priority group multibus all valid paths in 1 priority group group_by_serial 1 priority group per detected serial number group_by_prio 1 priority group per path priority value group_by_node_name 1 priority group per target node name getuid_callout Specifies the default program and arguments to call out to obtain a unique path ...

Page 29: ...s determined by the prio_callout program Currently there are priority callouts only for devices that use the group_by_prio path grouping policy which means that all the paths in a path group will always have the same priority If set to uniform all path weights are equal The default value is uniform no_path_retry A numeric value for this attribute specifies the number of times the system should att...

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Page 31: ...ultipath device you get a printout of the current device setup The format is as follows For each multipath device action_if_any alias wwid_if_different_from_alias size features hardware_handler For each path group _ scheduling_policy path_group_priority_if_known path_group_status_if_known For each path _ host channel id lun devnode major minor path_status dm_status_if_known For example the output ...

Page 32: ...ered from information in sysfs and the device mapper The ll option displays the information the l displays in addition to all other available components of the system When displaying the multipath configuration there are three verbosity levels you can specify with the v option of the multipath command Specifying v0 yields no output Specifying v1 outputs the created or updated multipath names only ...

Page 33: ...h1 253 3 mpath6p1 253 14 mpath7p1 253 13 mpath0 253 2 mpath7 253 9 mpath6 253 8 VolGroup00 LogVol01 253 1 mpath5 253 7 VolGroup00 LogVol00 253 0 mpath4 253 6 mpath1p1 253 10 mpath3 253 5 5 5 Troubleshooting with the multipathd Interactive Console The multipathd k command is an interactive interface to the multipathd daemon Entering this command brings up an interactive multipath console After ente...

Page 34: ...ng 24 The following command sequence ensures that multipath has picked up any changes to the multipath conf multipathd k reconfigure CTRL D Use the following command sequence to ensure that the path checker is working properly multipathd k show paths CTRL D ...

Page 35: ...25 Appendix A Revision History Revision History Revision 1 0 ...

Page 36: ...26 ...

Page 37: ...4 prio_callout parameter 14 18 product parameter 18 rr_min_io parameter 14 16 rr_weight parameter 14 16 18 selector parameter 14 udev_dir parameter 14 user_friendly_names parameter 13 14 vendor parameter 18 wwid parameter 16 configuring DM Multipath 7 D defaults section multipath conf file 13 dev mapper directory 5 dev mpath directory 5 device name 5 device mapper multipath package 7 devices addin...

Page 38: ...active console 23 multipathd daemon 3 multipathd start command 7 multipaths section multipath conf file 15 N no_path_retry parameter 14 16 18 P path_checker parameter 14 18 path_grouping_policy parameter 14 16 18 path_selector parameter 16 18 polling_interval parameter 14 prio_callout parameter 14 18 product parameter 18 R rr_min_io parameter 14 16 rr_weight parameter 14 16 18 S selector parameter...

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