Chapter 5. Managing Multipath I/O for Devices / 5.10. Scanning for New Devices without Rebooting
	5.9. Configuring Multipath I/O for an Existing Software RAID		5.11. Scanning for New Partitioned Devices without Rebooting

Scanning for New Devices without Rebooting

If your system has already been configured for multipathing and you later need to add more storage to the SAN, use the following procedure to scan the devices and make them available to multipathing without rebooting the system.

On the storage subsystem, use the vendor’s tools to allocate the device and update its access control settings to allow the Linux system access to the new storage. Refer to the vendor’s documentation for details.
On the Linux system, scan the SAN at a low level to discover the new devices. At a terminal console prompt, enter
```
echo 1 > /sys/class/fc_host/host<number>/issue_lip 
```
For example, to probe the HBA on host1, enter
```
echo 1 > /sys/class/fc_host/host1/issue_lip
```
At this point, the newly added device is not known to the higher layers of the Linux kernel's SCSI subsystem and is not yet usable.
Scan all targets for a host to make its new device known to the middle layer of the Linux kernel's SCSI subsystem. At a terminal console prompt, enter
```
echo "- - -" > /sys/class/scsi_host/host<number>/scan
```
For example, to probe the HBA on host1, enter
```
echo "- - -" > /sys/class/scsi_host/host1/scan
```

Check for scanning progress in the system log (the /var/log/messages file). At a terminal console prompt, enter

tail -30 /var/log/messages

This command displays the last 30 lines of the log. For example:

# tail -30 /var/log/messages

. . .

Feb 14 01:03 kernel: SCSI device sde: 81920000

Feb 14 01:03 kernel: SCSI device sdf: 81920000

Feb 14 01:03 multipathd: sde: path checker registered

Feb 14 01:03 multipathd: sdf: path checker registered

Feb 14 01:03 multipathd: mpath4: event checker started

Feb 14 01:03 multipathd: mpath5: event checker started

Feb 14 01:03:multipathd: mpath4: remaining active paths: 1

Feb 14 01:03 multipathd: mpath5: remaining active paths: 1

Repeat Step 2 through Step 4 to add paths through other HBA adapters on the Linux system that are connected to the new device.
Run the multipath command to recognize the devices for DM-MP configuration. At a terminal console prompt, enter
```
multipath
```
You can now configure the new device for multipathing.