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→Virtual Disk Images and Types
== Virtual Disk Images and Types ==
The most common method for providing disk storage to virtual machines is through the use of virtual disk image files. A virtual disk image file is nothing more than a file residing on the file system of the host which is treated by a virtual disk controller in the same way as a physical disk drive is used. The guest operating system interacts with this image through a virtual disk controller and is completely unaware of the fact that what it thinks is a physical hard disk drive is actually a file.
Virtual disk images can be created as either ''fixed-size'' or ''dynamically expanding'':
* '''Dynamically Expanding''' - The disk image file is created at a minimal size and then grows automatically as more space is needed by the guest operating system (up to a specified maximum). This has the advantage that disk space on the host is not used until it is needed, but can result in slower performance if the disk needs to be enlarged frequently.
* '''Fixed-size''' - The disk image file is created to the specified size. This pre-allocates all the requested disk space regardless of whether it is immediately needed, but results in improved disk write performance.
== Normal, Immutable and Write-Through Disk Images ==
