How to rescan the SCSI bus in Linux

You are in front of a Linux box, a VM really, with a bunch of new disks that must be configured and suddenly you remember that there is no ioscan in Linux, you will ask yourself, who is so stupid to create an operative system without ioscan?

Yes it is true, there is no ioscan in Linux and that means that every time you add a new disk to one of your virtual machine you have to reboot it, at least technically that is the truth. But don’t worry there is a quick and dirty way to circumvent that.

From a root shell execute the following command:

[root@redhat ~]# echo "- - -" > /sys/class/scsi_host/<host_number>/scan

After that if you do a fdsik -l will see the new disks.

If you want to rescan your box for new fiber channel disks the command is slightly different.

[root@redhat ~# echo "1" > /sys/class/fc_host/host#/issue_lip

For the fiber channel part there are also third party utilities. HP for example provides hp_rescan which comes with the Proliant Support Pack.

[root@redhat /]# hp_rescan -h
hp_rescan: rescans LUNs on HP supported FC adapters
Usage: hp_rescan -ailh[n]

-a: rescan all adapters
-i: rescan a specific adapter instance. The specific device should be a
 SCSI host number such as "0" or "6"
-l: lists all FC adapters
-n: do not perform "scsi remove-single-device" when executing probe-luns
-h: help
[root@redhat /]#

If you know other ways to rescan the SCSI bus in a Linux server please comment.

Juanma.