Chapter 1. Device Mapper Multipathing
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 multipath Command Options" . now includes entries for the -w and -W options of the multipath command, which allow you to better manage the wwids file. Additional options for the values argument of the features parameter in the multipath.conf file are documented in Chapter 4, The DM Multipath Configuration File . Table 4.1, "Multipath Configuration Defaults" . includes an entry for the force_sync parameter, 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 defaults section of the multipath.conf configuration file supports the new config_dir , new_bindings_in_boot , ignore_new_boot_devs , retrigger_tries , and retrigger_delays parameters. The defaults section of the multipath.conf file is documented in Table 4.1, "Multipath Configuration Defaults" . The defaults , devices , and multipaths sections of the multipath.conf configuration file now support the delay_watch_checks and delay_wait_checks configuration 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 multipathd command 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 the multipathd commands, 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 the pref bit 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 , and multipaths sections of the multipath.conf configuration file now support the skip_kpartx configuration 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 , and multipaths sections of the multipath.conf configuration file support the max_sectors_kb configuration parameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File . The defaults and devices sections of the multipath.conf configuration file support the detect_path_checker configuration parameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File . The defaults section of the multipath.conf configuration file supports the remove_retries and detect_path_checker parameters. The defaults section of the multipath.conf file 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 blacklist and blacklist_exceptions section of the multipath.conf configuration file support the property parameter. For information on the property parameter, see Section 4.2.6, "Blacklist Exceptions" . the defaults and multipaths sections of the multipath.conf file now support a value of file for the reservation_key parameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File . The defaults section of the multipath.conf configuration file supports the prkeys_file parameter. The defaults section of the multipath.conf file 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 blacklist section of the configuration file with a protocol section. 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 defaults and devices sections of the multipath.conf configuration file support the all_tg_pt parameter. For information on the configuration parameters, see Chapter 4, The DM Multipath Configuration File .