If you have added new storage to a running VM, you probably won’t see it. This is because the SCSI bus to which the storage devices are connected needs to be rescanned to make the new hardware visible.
How you rescan the SCSI bus depends on the operating system your Virtual Machine is running.
Instructions for common supported operating systems are as follows, these assume you have root or suitable privileges.
Linux, when adding a new disc
First find your host bus number
grep mpt /sys/class/scsi_host/host?/proc_name
Which should return a line like
where host0 is the relevant field.
use this to rescan the bus with the following command
echo "- - -" > /sys/class/scsi_host/host0/scan
In the above command the the hyphens represent controller,channel,lun, so – – – indicates all controllers, all channels and all luns should be scanned.
Linux, when expanding an existing disc
Assuming you know the device name of the disc you have expanded (eg /dev/sda) then you can simply issue the following command to force the rereading of the disk geometry. NOte that this is not 100% reliable with LVM on older kernels but should work with current kernels
echo 1 > /sys/class/scsi_device/device/rescan
Windows should pickup the change in discs regardless of you adding or expanding discs however if not you can either use the gui or the command line to force this. Note that expanding the boot device will typically always require a reboot, and will require you to boot from an alternative boot device (a boot CD image) to actually expand the windows boot partition. All these method assume you are an administrator on the system.
GUI method – Server 2003
Open Computer Management (Local).
In the console tree, click Computer Management (Local), click Storage, and then click Disk Management.
Click Action, and then click Rescan Disks.
GUI method server 2008
Open Server Manager.
In the tree pane, double-click the Storage node, and select Disk Management.
Right-click Disk Management and select Rescan Disks.
Command line method
as an administrator, start a command prompt and type
at the diskpart prompt, type
rescan Source: https://blogs.it.ox.ac.uk/oxcloud/2013/03/25/rescanning-your-scsi-bus-to-see-new-storage/