It is possible to add a new hard disk without a reboot. Whether or not it is a physical server where a physical disk was inserted into an available slot, or a new virtual disk was added to a VMware VM, the command structure to discover the new disk is the same.
First, take a look at the existing scsi devices using the lsscsi command:
~# lsscsi
[0:0:0:0] disk VMware Virtual disk 1.0 /dev/sda
[0:0:1:0] disk VMware Virtual disk 1.0 /dev/sdb
After adding a new vmdk or a new physical disk, /dev/sdc should pop in after running through the following sequence of commands in order to make the operating system aware of the new storage device.
The recommended command to do this, as per redhat documentation, is:
echo “c t l” > /sys/class/scsi_host/hosth/scan
From the lsscsi output above, this would translate into:
echo “0 2 0” > /sys/class/scsi_host/host0/scan
where host 0, channel 0, SCSI target ID 2, and LUN 0 are the next in-line / appropriate values:
The deprecated method was to submit a scsi command to /proc/scsi/scsi as follows, but does still work:
echo “scsi add-single-device 0 0 2 0” > /proc/scsi/scsi
If that’s not a comfortable option, then a rescan of the entire scsi bus for additional disks can be performed. Some systems have more than one scsi_host. With one command, they can all be rescanned as follows:
for host in $(ls -1d /sys/class/scsi_host/*); do echo “- – -” > ${host}/scan ; done
To rescan them individually, perform an ls in /sys/class/scsi_host and scan each one via a single command where # is the host number:
echo “- – -” > /sys/class/scsi_host/host#/scan
Note that in some distros of Linux, the kernel may recognize the new device once it has been added to the system, and the bus scan may not need to be performed. This would be validated by observing the output of lssci or by looking in syslog (/var/log/messages) for any indication of a newly added device. Something like the following would show up in the logs:
sd 0:0:2:0: Attached scsi disk sdc
This matches up nicely with lsscsi output:
~# lsscsi
[0:0:0:0] disk VMware Virtual disk 1.0 /dev/sda
[0:0:1:0] disk VMware Virtual disk 1.0 /dev/sdb
[0:0:2:0] disk VMware Virtual disk 1.0 /dev/sdc
Next, the new device can be partitioned, labeled, create a file system, and mounted.
echo -e -n “o\nn\np\n1\n\n\nw\n” | fdisk /dev/sdc > /dev/null 2>&1
mkfs.ext3 /dev/sdc1
mkdir /data
e2label /dev/sdc1 /data
vi /etc/fstab
mount -a
On the flip side of the coin, a device may be deleted using the following command:
# echo 1 > /sys/block/devName/device/delete (where devName is the device name to be removed, for example sdc in the following line)
# echo 1 > /sys/block/sdc/device/delete
Another variation of this operation is echo 1 > /sys/class/scsi_device/h:c:t:l/device/delete
A deprecated method of the above command is:
# echo “scsi remove-single-device 0 0 2 0” > /proc/scsi/scsi
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