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KVM - Add Disk

I run my virtual machines on SSD storage which is expensive compared to traditional HDD storage. Thus if a virtual machine needs a lot of storage, such as for a mirror, then I will give it an HDD disk to put the data on. Here's how to do just that.

Create the Disk

qemu-img create -f qcow2 -o preallocation=metadata \
[filepath] [size]G

Attach the Disk

virsh attach-disk [vm ID] \
--source /path/to/disk.qcow2 \
--target vd[x] \
--persistent

The previous command can be run to attach the disk whilst the VM Is running.

The path to the disk for source has to be an absolute path, not a relative one.

At this point the disk should show up in your VM if you run the command:

ls /dev/vd*

To use the disk we need to create a filesystem on it.

sudo mkfs -t ext4 /dev/vd[x]

Now we need a place to mount the disk and add it to our /etc/fstab so that it will mount on boot.

sudo mkdir /media/data

Then add the following to your fstab

/dev/vdb /media/data ext4 defaults 0 2

Now you can mount everything

sudo mount -a