failover(7M)
failover - disk device alternate path support
As shipped in IRIX 6.5.7. Last changed in IRIX 6.5.7.
NAME failover - disk device alternate path support SYNOPSIS /etc/init.d/failover [init|start] DESCRIPTION Failover is the ability to define and manage alternate paths to a single disk device or lun. At startup, failover automatically detects and configures alternate paths to SGI K5 RAID devices. To configure primary and alternate paths to other more generic devices, failover also processes configuration directives contained within the /etc/failover.conf configuration file. Failover works in conjuction with the SGI logical volume manager, to automatically switch between primary and alternate paths. Additionally, failover is only possible for devices which utilize dksc(7m), the scsi disk driver. Failover uses /sbin/foconfig to parse the configuration file and direct the creation of failover groups. /sbin/foconfig should not be executed directly. Alternate Path Configuration Primary and alternate paths to devices are defined by two different mechanisms. Automatic detection, and definition within a configuration file. Configuration of SGI K5 RAID devices is automatic and happens at the time of device discovery during the probing of the scsi and fibre channel buses, making use of the dual storage processors. Any path to the active storage processor can be used for I/O requests unless explicit primary configuration is used (see "Using Manual Configuration with SGI K5" below). Configuration of alternate paths to other disk storage devices is defined within the /etc/failover.conf configuration file. This file is processed during failover startup, and when the /etc/init.d/failover script is executed. When /etc/init.d/failover is executed with the start parameter, it automatically calls xlv_assemble(1m). When executed with the init parameter, the execution of xlv_assemble is skipped. An entry defining the available paths to a device consists of a single line, or multiple lines, all except the last ending in a \ (backslash). An entry defines an arbitrary group name, a primary path, and up to fifteen alternate paths. The group name is an arbitrary string of up to 31 characters. Following the group name are the /dev/scsi names associated with the primary and alternate paths, the primary being the first path specified. With manual configuration, only the primary path to an I/O device can be used for I/O requests. This is also the case if the configuration file is used to explicitly specify a primary path to an SGI K5 RAID. Using Manual Configuration with SGI K5 SGI K5 RAID devices can use the /etc/failover.conf configuration file to explicitly specify primary paths, rather than letting a volume manager pick one. This is useful, because if multiple controllers can each access the same storage (in a SAN environment), volume managers will tend to use a single controller to access all storage connected to a given storage network, precluding using different host adapters to access different devices on the storage network. Specifying a primary allows the administrator to choose different host adapters to access different storage devices, because the volume manager will not be able to access storage through the alternate paths. This is particularly useful when striping. Only the primary path needs to be specified in the /etc/failover.conf file with this option. Alternate paths will be automatically detected. Sample Configuration Entries The sample file shows failover groups, each consisting of a primary path and one or more alternate paths. The sample also includes the comments placed in the sample configuration file which is installed on the system. #ident $Revision: 1.6 $ # # This is the configuration file for table driven failover support. # The entries within this file consist of a single line per # failover grouping. These lines describe up to four paths to # each device. Obviously, these paths should reference the # same device! Some sanity checking is performed, but the # software is not foolproof in this area. (If it was foolproof, # the configuration file would be unnecessary!) It is recommended # that all paths to a device be listed. # # The format of each line consists of a group name followed by # up to four device names from the "/dev/scsi" directory. If # it's not in "/dev/scsi", it cannot be configured. But, this # implementation assumes that if a device is not present, its # path has failed. Consequently, no error messages will be # generated for missing paths. This means that you may have a # a failover group that consists of a single primary path with # no alternates. # # Additionally, there is a configuration directive available that # will cause the program to emit debug information. Placing # "#verbose" at the start of a line, without the quotes, will # enable the debug output. The debug output is displayed for # all subsequent configuration directives. Once enabled, the # debug output cannot be disabled. # # Lines that begin with a "#" are considered comment lines. # A "#" anywhere within a line signals the beginning of a comment. # White space must separate the last parameter of a line and the #. # Blank lines are also considered a comment. # # --> Lines that begin with 'sc' will be skipped as it's likely a # --> configuration error. # # Sample configuration. (Remember to omit the "#" the start of # the line.) # # # # Name Pri path | alt path | alt path | alt path # # GroupA sc6d50l0 sc7d50l0 sc8d50l0 sc9d50l0 # GroupB sc6d51l0 sc7d51l0 sc8d51l0 sc9d51l0 # Some comment # GroupC sc6d52l0 sc7d52l0 sc8d52l0 sc9d52l0 # # One word of caution. The switch to an alternate path is # choreographed by the SGI logical volume manager. An SGI logical # volume manager is a requirement for failover to function. XLV # is an SGI logical volume manager. # # Notes: # # It is not possible to change the primary device of a group after # the initial configuration by reordering the entries on the line # and running /etc/init.d/failover start. To change the primary, # scsifo may be used to switch to the next available path. # # It is not possible to remove the primary of a group by deleting # the entry from the group and running /etc/init.d/failover start. # A reboot is necessary. # # The "DOWN" displayed by hinv for the failed path will be removed by any # successful access, whether by probing (scsiha(1m) -p), ioconfig(1m), # a successful inquiry performed as a result of accessing the /dev/scsi # device (such as with scsicontrol(1m)), or the /dev/dsk devices, etc. # Note the a disk open may fail, but if the inquiry done at disk open # time succeeds, the "DOWN" indicator will still be removed. # A sc7d1l0 sc8d1l0 B sc7d1l1 sc8d1l1 C sc7d1l2 sc8d1l2 D sc7d1l3 sc8d1l3 E sc7d1l4 sc8d1l4 F sc7d1l5 sc8d1l5 G sc7d1l6 sc8d1l6 H sc7d1l7 sc8d1l7 I 2000002037003be2/lun0/c3p1 2000002037003be2/lun0/c5p2 J 2000002037003c6c/lun0/c5p2 2000002037003c6c/lun0/c3p1 lun16 2000006016fe0cc0/lun16/c104p0 2000006016fe0cc0/lun16/c108p0 \ 2000006016fe0cc0/lun16/c110p0 2000006016fe0cc0/lun16/c109p0 \ 2000006016fe0cc0/lun16/c107p0 2000006016fe0cc0/lun16/c106p0 \ 2000006016fe0cc0/lun16/c105p0 2000006016fe0cc0/lun16/c103p0 Switching to an Alternate Path Failover is controlled by the SGI logical volume manager. When the logical volume manager receives notification of an i/o error, it requests failover to switch the erring device to an available alternate path. If the path switch is successful, the SGI logical volume manager retries the failed i/o using the new path. The scsifo(1m) command is available to permit the system administrator to manually request a switch to an alternate path. While the scsifo command performs a switch, it is not detected by the SGI logical volume manager until the SGI logical volume manager receives an i/o error on the current path due to the path no longer being available. The SGI logical volume manager then begins utilizing the new path. Inventory Display The hinv(1m) command will display the path status of primary and alternate paths configured in the /etc/failover.conf configuration file. The following sample hinv output reflects the above sample configuration file. Three of the devices have failed over to the alternate path, perhaps via the scsifo command. Integral SCSI controller 7: Version Fibre Channel AIC-1160, revision 1 Disk drive: unit 1 on SCSI controller 7 (primary path) Disk drive: unit 1,lun 1, on SCSI controller 7 (primary path) Disk drive: unit 1,lun 2, on SCSI controller 7 (primary path) Disk drive: unit 1,lun 3, on SCSI controller 7 (primary path) Disk drive: unit 1,lun 4, on SCSI controller 7 (primary path) Disk drive: unit 1,lun 5, on SCSI controller 7 (alternate path) DOWN Disk drive: unit 1,lun 6, on SCSI controller 7 (alternate path) DOWN Disk drive: unit 1,lun 7, on SCSI controller 7 (alternate path) DOWN Integral SCSI controller 8: Version Fibre Channel AIC-1160, revision 1 Disk drive: unit 1 on SCSI controller 8 (primary path) Disk drive: unit 1,lun 1, on SCSI controller 8 (alternate path) Disk drive: unit 1,lun 2, on SCSI controller 8 (alternate path) Disk drive: unit 1,lun 3, on SCSI controller 8 (alternate path) Disk drive: unit 1,lun 4, on SCSI controller 8 (alternate path) Disk drive: unit 1,lun 5, on SCSI controller 8 (primary path) Disk drive: unit 1,lun 6, on SCSI controller 8 (primary path) Disk drive: unit 1,lun 7, on SCSI controller 8 (primary path) Integral SCSI controller 3: Version Fibre Channel QL2200 Fabric Disk: node 2000002037003be2 port 1 lun 0 on SCSI controller 3 (primary path) Fabric Disk: node 2000002037003c6c port 1 lun 0 on SCSI controller 3 (alternate path) Integral SCSI controller 5: Version Fibre Channel QL2200 Fabric Disk: node 2000002037003be2 port 2 lun 0 on SCSI controller 5 (alternate path) Fabric Disk: node 2000002037003c6c port 2 lun 0 on SCSI controller 5 (primary path) By using the scsiha(1m) command to reprobe the bus to which a down device is connected, presuming the device is now responding on the bus, the "DOWN" indicator displayed by hinv can be cleared. FILES /etc/failover.conf /etc/init.d/failover /etc/init.d/xlv /var/sysgen/master.d/failover SEE ALSO autoconfig(1m), dks(5m), ds(7m), hinv(1m), ioconfig(1m), scsifo(1m), scsiha(1m), xlv_assemble(1m), and xlv(7m). NOTES The group name specified within the /etc/failover.conf file has no external visibility. It cannot be correlated to the group number information displayed by the scsifo command.