A virtual disk is a storage abstraction that provides the functionality of a physical hard drive without being directly tied to a physical device. Instead, it exists as a file (or series of files) on the host system’s storage, and it’s used by virtual machines (VMs) as though it were a physical disk. This approach allows VMs to run operating systems, applications, and store data just as if they were on a physical machine.
Here are some key aspects of virtual disks:
File-Based: Virtual disks are typically stored as files on the host system. Depending on the virtualization platform, these might be VMDK files (VMware), VHD/VHDX files (Microsoft Hyper-V), QCOW2 files (QEMU/KVM), among others.
Configurable Size: When creating a virtual disk, users can define its size. The virtual disk will then appear to the VM as a hard drive of that specified size.
Dynamic vs. Fixed Size: Virtual disks can be created as either dynamic (thin-provisioned) or fixed (thick-provisioned) size:
- Dynamic (Thin-Provisioned): The disk file starts small and grows as data is added, up to the maximum size defined when the disk was created.
- Fixed (Thick-Provisioned): The disk file occupies the full specified size right from the beginning, regardless of how much data is actually stored on it.
Snapshot Support: Many virtualization platforms allow for snapshots of virtual machines. These snapshots capture the current state of a VM, including the contents of its virtual disk(s). This facilitates quick recovery to a prior state if needed.
Portability: Since virtual disks are file-based, they are portable. This means they can be moved, copied, or backed up just like any other file. This portability also simplifies tasks like migrating a VM from one host to another.
Disk Operations: Just like physical disks, virtual disks can be partitioned, formatted, and encrypted within the VM. They can also be resized, cloned, or converted between different formats on the host side using virtualization management tools.
Performance: While virtual disks provide great flexibility, there’s often some overhead because of the additional layer of abstraction. However, with modern hardware, virtualization optimizations, and proper configuration, the performance impact can be minimized.
In summary, virtual disks offer a flexible and manageable way of handling storage in a virtualized environment, allowing VMs to operate as if they have their own dedicated storage resources.