I currently support a number of Linux hosts that run inside VMWare vSphere server. Periodically I need to add new storage devices to these hosts, which requires me to login to the vSphere client and add the device through the “edit settings” selection. The cool thing about vSphere is that the LUNs are dynamically added to the guest, and the guest will see the devices once the SCSI bus has been scanned. There are several ways to scan for storage devices, but the simplest way I’ve found is to use the rescan-scsi-bus.sh shell script that comes with the sg3_utils package.
To use rescan-scsi-bus.sh, you will first need to install the sg3_utils package:
$ yum install sg3_utils
Once installed, you can run fdisk or lsscsi to view the devices on your system:
$ lsscsi
[0:0:0:0] disk VMware Virtual disk 1.0 /dev/sda
[1:0:0:0] disk VMware Virtual disk 1.0 /dev/sdb
$ fdisk -l
Disk /dev/sda: 9663 MB, 9663676416 bytes
255 heads, 63 sectors/track, 1174 cylinders
Device Boot Start End Blocks Id System
/dev/sda2 652 1173 4192965 82 Linux swap / Solaris
Disk /dev/sdb: 19.3 GB, 19327352832 bytes
255 heads, 63 sectors/track, 2349 cylinders
Device Boot Start End Blocks Id System
/dev/sdb1 1 2349 18868311 83 Linux
As you can see above, we currently have two physical devices connected to the system. To scan for a new device I just added, we can run rescan-scsi-bus.sh from the host:
$ /usr/bin/rescan-scsi-bus.sh -r
Host adapter 0 (mptspi) found.
Host adapter 1 (mptspi) found.
Scanning SCSI subsystem for new devices
and remove devices that have disappeared
Scanning host 0 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs
Scanning for device 0 0 0 0 ...
OLD: Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: VMware Model: Virtual disk Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 02
Scanning host 1 channels 0 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs
Scanning for device 1 0 0 0 ...
OLD: Host: scsi1 Channel: 00 Id: 00 Lun: 00
Vendor: VMware Model: Virtual disk Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 02
Scanning for device 1 0 1 0 ...
NEW: Host: scsi1 Channel: 00 Id: 01 Lun: 00
Vendor: VMware Model: Virtual disk Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 02
Scanning for device 1 0 1 0 ...
OLD: Host: scsi1 Channel: 00 Id: 01 Lun: 00
Vendor: VMware Model: Virtual disk Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 02
0 new device(s) found.
0 device(s) removed.
The scan output will show you the devices it finds, and as you can see above, it was able to locate 3 “Virtual disk” drives. To verify the machine sees the drives, we can run lsscsi and fdisk again:
$ lsscsi
[0:0:0:0] disk VMware Virtual disk 1.0 /dev/sda
[1:0:0:0] disk VMware Virtual disk 1.0 /dev/sdb
[1:0:1:0] disk VMware Virtual disk 1.0 /dev/sdc
$ fdisk -l
Disk /dev/sda: 9663 MB, 9663676416 bytes
255 heads, 63 sectors/track, 1174 cylinders
Device Boot Start End Blocks Id System
/dev/sda2 652 1173 4192965 82 Linux swap / Solaris
Disk /dev/sdb: 19.3 GB, 19327352832 bytes
255 heads, 63 sectors/track, 2349 cylinders
Device Boot Start End Blocks Id System
/dev/sdb1 1 2349 18868311 83 Linux
Disk /dev/sdc: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Disk /dev/sdc doesn't contain a valid partition table
There are various solutions to check for new SCSI devices (Emulex has a tool, QLogic has a tool, you can scan for devices by hand, etc.), the rescan script has proven to be the easiest solution for me. Since I didn’t write the rescan script, use this information at your own risk. It should work flawlessly, but you’re on your own when you run it!