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VirtualBox虚拟机安装Debian 9.2.1图文详解

Do not add a virtual hard disk
Create a virtual hard disk now
Use an existing virtual hard disk file

VDI(VirtualBox 磁盘映像)
VHD(虚拟硬盘)
VMDK(虚拟磁盘)

: http://www.linuxidc.com/Linux/2017-11/148909p2.htm