Oh this was a really old post that I've found among my forgotten files, but it's pure gold if you find yourself working with legacy machinses so it deserves to be here. I haven't tested this in AWS, but I just might and update the text afterwards.
It is quite common practice when adding a new drive to a Linux system to reboot the system afterwards so that the server can re-scan its hardware and detect the change. However, every now and then we get to make changes to a server that we don't want to reboot it for some reason. Or maybe you are lazy, like me and don't want to wait 1 min to reboot. In any case, bellow is a way to make your system re-scan the hardware and detect the changes.
TL;DR
If you are in a hurry and don't want to read all than you can use the bellow command to re-scan the SCSI controller and detect the newly added disk.:
$ sudo echo "- - -" > /sys/class/scsi_host/host0/scan
If you don't know the location of the new disk, than you can also re-scan all of the SCSI controllers:
$ ls /sys/class/scsi_host/ | while read host ; do echo "- - -" > /sys/class/scsi_host/$host/scan ; done
If you want to learn more then continue on with the tutorial.
In this example I assume that you are working on a VM with SCSI adapters.
If you take a look into /sys/class/scsi_host you can find sim-links pointing to all of the SCSI adapters available (including those which are not yet installed). From the output bellow, we can see that this particular VM can support up to 32 SCSI adapters, and each SCSI adapter can support up to 7 disks.
# ls -l /sys/class/scsi_host/
total 0
lrwxrwxrwx 1 root root 0 Feb 13 21:09 host0 -> ../../devices/pci0000:00/0000:00:10.0/host0/scsi_host/host0
lrwxrwxrwx 1 root root 0 Feb 13 21:09 host1 -> ../../devices/pci0000:00/0000:00:07.1/ata1/host1/scsi_host/host1
lrwxrwxrwx 1 root root 0 Feb 13 21:09 host10 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/ata10/host10/scsi_host/host10
lrwxrwxrwx 1 root root 0 Feb 13 21:09 host11 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/ata11/host11/scsi_host/host11
...
Output omited
...
lrwxrwxrwx 1 root root 0 Feb 13 21:09 host31 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/ata31/host31/scsi_host/host31
lrwxrwxrwx 1 root root 0 Feb 13 21:09 host32 -> ../../devices/pci0000:00/0000:00:11.0/0000:02:05.0/ata32/host32/scsi_host/host32
And so on up to ... ... /host32/scan
If your server is a VM then there is a high probability that the new disk will be attached to host0. If you have access to the hypervisor or if you use software hypervisor like VMware Workstation or a VirtualBox than you can see to which SCSI adapter the disk is attached by looking at the hardware options for the VM.
In the below example I've looked at the 4th disk Advanced options and I can see that it is attached to the SCSI0 controller on its 3rd connector.
Note: This VM is still ON, as that is the reason why I can't change the disk location.
Now, lets continue on further. I still haven't added a new disk as I was giving the explanation. Lets see what we currently have on our VM:
# fdisk -l
Disk /dev/sda: 17.2 GB, 17179869184 bytes, 33554432 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000c481a
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 1050623 524288 83 Linux
/dev/sda2 1050624 33554431 16251904 83 Linux
Disk /dev/sdb: 17.2 GB, 17179869184 bytes, 33554432 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000eeba8
Device Boot Start End Blocks Id System
/dev/sdb1 2048 33554431 16776192 83 Linux
Disk /dev/sdc: 34.4 GB, 34359738368 bytes, 67108864 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x00098f97
Device Boot Start End Blocks Id System
/dev/sdc1 2048 67108863 33553408 83 Linux
Disk /dev/sdd: 4294 MB, 4294967296 bytes, 8388608 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000782c3
Device Boot Start End Blocks Id System
/dev/sdd1 2048 8194047 4096000 82 Linux swap / Solaris
Disk /dev/sde: 17.2 GB, 17179869184 bytes, 33554432 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x770ab37c
Device Boot Start End Blocks Id System
/dev/sde1 2048 33554431 16776192 83 Linux
I have 5 disks in total:
/dev/sda
/dev/sdb
/dev/sdc
/dev/sdd
/dev/sde
Using the Workstation Console, I will add a new disk.
In order to force the system to scan those periferials we can make use of the command:
$ echo "- - -" > /sys/class/scsi_host/host0/scan
And after that we will spot the new disk /dev/sdf with the fdisk command:
# fdisk -l
Disk /dev/sda: 17.2 GB, 17179869184 bytes, 33554432 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000c481a
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 1050623 524288 83 Linux
/dev/sda2 1050624 33554431 16251904 83 Linux
...
Some output omited
...
Disk /dev/sde: 17.2 GB, 17179869184 bytes, 33554432 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x770ab37c
Device Boot Start End Blocks Id System
/dev/sde1 2048 33554431 16776192 83 Linux
Disk /dev/sdf: 21.5 GB, 21474836480 bytes, 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
If you don't have access to the hypervisor then you can rescan all of the SCSI adapters using this simple inline script:
$ ls /sys/class/scsi_host/ | while read host ; do echo "- - -" > /sys/class/scsi_host/$host/scan ; done