Chapter 1. Device Mapper Multipathing
Device mapper multipathing (DM Multipath) allows you to configure multiple I/O paths between server nodes and storage arrays into a single device. These I/O paths are physical SAN connections that can include separate cables, switches, and controllers. Multipathing aggregates the I/O paths, creating a new device that consists of the aggregated paths.
This chapter provides a summary of the features of DM-Multipath that were added subsequent to the initial release of Red Hat Enterprise Linux 7. Following that, this chapter provides a high level overview of DM Multipath and its components, as well as an overview of DM-Multipath setup.
1.1. New and Changed Features
This section lists features of the DM Multipath that are new since the initial release of Red Hat Enterprise Linux 7.
1.1.1. New and Changed Features for Red Hat Enterprise Linux 7.1
Red Hat Enterprise Linux 7.1 includes the following documentation and feature updates and changes.
- Table 5.1, “Useful
multipathCommand Options”. now includes entries for the -w and -W options of themultipathcommand, which allow you to better manage the wwids file. - Additional options for the
valuesargument of thefeaturesparameter in themultipath.conffile are documented in Chapter 4, The DM Multipath Configuration File. - Table 4.1, “Multipath Configuration Defaults”. includes an entry for the
force_syncparameter, which prevents path checkers from running in async mode when set to "yes".
In addition, small technical corrections and clarifications have been made throughout the document.
1.1.2. New and Changed Features for Red Hat Enterprise Linux 7.2
Red Hat Enterprise Linux 7.2 includes the following documentation and feature updates and changes.
- This document includes a new section, Section 5.1, “Automatic Configuration File Generation with Multipath Helper”. The Multipath Helper application gives you options to create multipath configurations with custom aliases, device blacklists, and settings for the characteristics of individual multipath devices.
- The
defaultssection of themultipath.confconfiguration file supports the newconfig_dir,new_bindings_in_boot,ignore_new_boot_devs,retrigger_tries, andretrigger_delaysparameters. Thedefaultssection of themultipath.conffile is documented in Table 4.1, “Multipath Configuration Defaults”. - The
defaults,devices, andmultipathssections of themultipath.confconfiguration file now support thedelay_watch_checksanddelay_wait_checksconfiguration parameters. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File.
In addition, small technical corrections and clarifications have been made throughout the document.
1.1.3. New and Changed Features for Red Hat Enterprise Linux 7.3
Red Hat Enterprise Linux 7.3 includes the following documentation and feature updates and changes.
- The
multipathdcommand supports new format commands that show the status of multipath devices and paths in "raw" format versions. In raw format, no headers are printed and the fields are not padded to align the columns with the headers. Instead, the fields print exactly as specified in the format string. For information on themultipathdcommands, see Section 5.11, “The multipathd Commands”. - As of Red Hat Enterprise Linux 7.3, if you specify
prio "alua exclusive_pref_bit"in your device configuration, multipath will create a path group that contains only the path with theprefbit set and will give that path group the highest priority. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File. - The
defaults,devices, andmultipathssections of themultipath.confconfiguration file now support theskip_kpartxconfiguration parameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File.
In addition, small technical corrections and clarifications have been made throughout the document.
1.1.4. New and Changed Features for Red Hat Enterprise Linux 7.4
Red Hat Enterprise Linux 7.4 includes the following documentation and feature updates and changes.
- The
defaults,devices, andmultipathssections of themultipath.confconfiguration file support themax_sectors_kbconfiguration parameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File. - The
defaultsanddevicessections of themultipath.confconfiguration file support thedetect_path_checkerconfiguration parameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File. - The
defaultssection of themultipath.confconfiguration file supports theremove_retriesanddetect_path_checkerparameters. Thedefaultssection of themultipath.conffile is documented in Table 4.1, “Multipath Configuration Defaults”.
1.1.5. New and Changed Features for Red Hat Enterprise Linux 7.5
Red Hat Enterprise Linux 7.5 includes the following documentation and feature updates and changes.
- As of Red Hat Enterprise Linux 7.5, the
blacklistandblacklist_exceptionssection of themultipath.confconfiguration file support thepropertyparameter. For information on thepropertyparameter, see Section 4.2.6, “Blacklist Exceptions”. - the
defaultsandmultipathssections of themultipath.conffile now support a value offilefor thereservation_keyparameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File. - The
defaultssection of themultipath.confconfiguration file supports theprkeys_fileparameter. Thedefaultssection of themultipath.conffile is documented in Table 4.1, “Multipath Configuration Defaults”.
1.1.6. New and Changed Features for Red Hat Enterprise Linux 7.6
Red Hat Enterprise Linux 7.6 includes the following documentation and feature updates and changes.
- As of Red Hat Enterprise Linux 7.6, you can specify the protocol for a device to be excluded from multipathing in the
blacklistsection of the configuration file with aprotocolsection. For information on blacklisting by device protocol, see Section 4.2.5, “Blacklisting By Device Protocol (Red Hat Enterprise Linux 7.6 and Later)”. - The
defaultsanddevicessections of themultipath.confconfiguration file support theall_tg_ptparameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File.
