Red Hat ENTERPRISE LINUX 5.5 - ONLINE STORAGE GUIDE Manual page 13

the storage server. If this is not the case, note the World Wide Port Name (WWPN) for each port that
will be used to access the new LUN.
Next, make the operating system aware of the new storage device, or path to an existing device. The
recommended command to use is:
echo "c t l" > /sys/class/scsi_host/hosth/scan
In the previous command, h is the HBA number, c is the channel on the HBA, t is the SCSI target ID,
and l is the LUN.
Note
The older form of this command, echo "scsi add-single-device 0 0 0 0" > /
proc/scsi/scsi, is deprecated.
For Fibre Channel storage servers that implement a single WWNN for all ports, you can determine the
correct h,c,and t values (i.e. HBA number, HBA channel, and SCSI target ID) by searching for the
WWNN in sysfs. For example, if the WWNN of the storage server is 0x5006016090203181, use:
grep 5006016090203181 /sys/class/fc_transport/*/node_name
This should display output similar to the following:
/sys/class/fc_transport/target5:0:2/node_name:0x5006016090203181
/sys/class/fc_transport/target5:0:3/node_name:0x5006016090203181
/sys/class/fc_transport/target6:0:2/node_name:0x5006016090203181
/sys/class/fc_transport/target6:0:3/node_name:0x5006016090203181
This indicates there are four Fibre Channel routes to this target (two single-channel HBAs, each
leading to two storage ports). Assuming a LUN value is 56, then the following command will configure
the first path:
echo "0 2 56" > /sys/class/scsi_host/host5/scan
This must be done for each path to the new device.
For Fibre Channel storage servers that do not implement a single WWNN for all ports, you can
determine the correct HBA number, HBA channel, and SCSI target ID by searching for each of the
WWPNs in sysfs.
Another way to determine the HBA number, HBA channel, and SCSI target ID is to refer to another
device that is already configured on the same path as the new device. This can be done with various
commands, such as lsscsi, scsi_id, multipath -l, and ls -l /dev/disk/by-*. This
information, plus the LUN number of the new device, can be used as shown above to probe and
configure that path to the new device.
After adding all the SCSI paths to the device, execute the multipath command, and check to see
that the device has been properly configured. At this point, the device can be added to md, LVM,
mkfs, or mount, for example.
If the steps above are followed, then a device can safely be added to a running system. It is not
necessary to stop I/O to other devices while this is done. Other procedures involving a rescan (or
a reset) of the SCSI bus, which cause the operating system to update its state to reflect the current
device connectivity, are not recommended while storage I/O is in progress.
Adding a Storage Device or Path
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