Chapter 28. 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
Example 28.1. WWID
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.
user_friendly_names, then additional steps are required to obtain consistent names in a cluster. Refer to the Consistent Multipath Device Names in a Cluster section in the Using DM Multipath Configuration and Administration book.
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.