HP StorageWorks Secure Path V3.0C for Linux and Linux Workgroup Edition Installation and Reference Guide (AA-RU7VD-TE, February 2004)

Fibre Channel Device Software
114 Secure Path v3.0C for Linux and Linux Workgroup Edition Installation and Reference Guide
Using Secure Path Persistence Software
Linux SCSI layer overview
The Linux operating system does not provide built-in LUN persistence. Lack of
LUN persistence means that if you add or delete physical LUNs or disks and
reboot your system, there is a probability that the device mnemonics will change
in an undesirable way. Table 12 shows a system with three LUNs displayed:
In this example, /dev/sdb is not needed anymore and needs to be removed. So,
the disk is unmounted and removed. At some point, the system is rebooted and
failed to mount /dev/sdc the new data disk.
Upon further analysis, the system now thinks that new data disk is /dev/sdb.
This situation occurs frequently, due to the way physical buses are scanned and
device mnemonics are bound to them.
When the system is first booted, the buses are scanned for devices in the order by
which they are detected. Devices are scanned on a bus starting at LUN 0 and up.
Device mnemonics are assigned in order starting with sda until all the
major/minor numbers are exhausted.
Because /dev/sdb was deleted from the system, on the next boot, /dev/sdc
was reassigned to /dev/sdb. This is not desirable behavior.
Table 12: System displaying three LUNs
Device name Bus-Target-LUN Disk content
/dev/sda Bus 0 Target 0 LUN 0 System disk
/dev/sdb Bus 0 Target 0 LUN 1 Obsolete data
/dev/sdc Bus 0 Target 0 LUN 2 New data