You can easily manage datadisks of your VPS. Total amount of space available for your VPS depends on the VPS offering you are using. It is described in VPS hosting offerings. When you deploy a VPS you get ROOT disk. It is main bootable disk for your VPS. However its size is defined in template. To use the rest available space you can create a datadisk (datadisks) and attach it to your VPS.
For example if you purchase small-VPS you can use 30 Gb of total space. When you deploy CentOS template the size of the ROOT volume is only 8Gb. So you can create additional volume (datadisk) 22Gb and attach it to your VPS. In *nix OS you will see it as /dev/vdx device (for example /dev/vda). Or if you want you can create several datadisks with total size up to 22Gb.
Windows VPS. While using Windows VPS you get 50Gb of disk space irrespective of VPS you are using. This is the size of root volume you get when you Deploy Windows VPS template.
You can manage your datadisks only for deployed VPS.
While in "Managing VPS" menu click "Show hard disk drive". You will get to volumes control screen.
To create a datadisk volume click "Add volume". Enter size and description for the volume and click "Done".
Now you have created Volume and you can attach it to your VPS.
You won't be able to use a volume without attaching it to VPS
You can see the status of volumes (Attached/Detached). To attach/detach volume press corresponding button.
You cannot attach/detach root volume
To destroy a volume detach it from your VPS and then press Delete button. Be aware that volume will be erased and all information in this volume will be lost!