Disk and block I/O tuning

We will start with disk options, transport, and image formats. Later we move onto block I/O tuning.

The virtual disk of a VM can be either block device or image file.

For better VM performace a block device based virtual disk is preferred over a image file that resides on a remote file system like NFS, GlusterFS, etc. However, we cannot ignore that the file backend helps the virt admin to better manage guest disks and it is immensely helpful in some scenarios. From our experience, we have noticed most users make use of disk image files, especially when performance is not much of a concern. Keep in mind that the total number of virtual disks that can be attached to a VM has a limit. At the same time, there is no restriction on mixing and using block devices and files and using them as storage disks for the same guest.

As mentioned earlier, a guest treats the virtual disk as its storage. When an application inside a guest operating system writes data to the local storage...