1.3. Persistent Naming
- PCI identifier of the host bus adapter (HBA)
- channel number on that HBA
- the remote SCSI target address
- the Logical Unit Number (LUN)
/dev/sdname; another is the
major:minornumber. A third is a symlink maintained in the
/dev/disk/by-path/directory. This symlink maps from the path identifier to the current
/dev/sdname. For example, for a Fibre Channel device, the PCI info and
Host:BusTarget:LUNinfo may appear as follows:
pci-0000:02:0e.0-scsi-0:0:0:0 -> ../../sda
by-path/names map from the target name and portal information to the
0x83) or Unit Serial Number (page
0x80). The mappings from these WWIDs to the current
/dev/sdnames can be seen in the symlinks maintained in the
0x83identifier would have:
scsi-3600508b400105e210000900000490000 -> ../../sda
0x80identifier would have:
scsi-SSEAGATE_ST373453LW_3HW1RHM6 -> ../../sda
/dev/sdname on that system. Applications can use the
/dev/disk/by-id/name to reference the data on the disk, even if the path to the device changes, and even when accessing the device from different systems.
/dev/mapper/wwid, such as
multipath -lshows the mapping to the non-persistent identifiers:
/dev/sdname, and the
3600508b400105df70000e00000ac0000 dm-2 vendor,product [size=20G][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=0][active] \_ 5:0:1:1 sdc 8:32 [active][undef] \_ 6:0:1:1 sdg 8:96 [active][undef] \_ round-robin 0 [prio=0][enabled] \_ 5:0:0:1 sdb 8:16 [active][undef] \_ 6:0:0:1 sdf 8:80 [active][undef]
/dev/sdname on the system. These names are persistent across path changes, and they are consistent when accessing the device from different systems.
user_friendly_namesfeature (of device-mapper-multipath) is used, the WWID is mapped to a name of the form
/dev/mapper/mpathn. By default, this mapping is maintained in the file
mpathnnames are persistent as long as that file is maintained.
/var/lib/multipath/bindings) must be available at boot time. If
/varis a separate filesystem from
/, then you must change the default location of the file. For more information, refer to http://kbase.redhat.com/faq/docs/DOC-17650.
udevrules to implement persistent names of your own, mapped to the WWID of the storage. For more information about this, refer to http://kbase.redhat.com/faq/docs/DOC-7319.