The virtual machine (VM) requires storage for its data, program and system files. To improve the overall performance of the VM, an administrator can utilize virtual storage to display a single network-based or physical storage device in multiple types of storage. The VM can access it without needing to know the underlying hardware.
Virtual storage management requires a careful balance between performance, capacity and costs. Administrators must decide if they want to use only solid-state drives, or hard-drive disks. They must also decide what kind of storage controllers and the number of controllers to install. To control costs, IT managers should think about storage reduction capabilities such as deduplication and compression.
There are three kinds of virtual storage: physical disks, RAID groups and logical volume (LV). Physical disks and RAID group divide the physical capacity into smaller units that servers or applications see as one storage device. A virtualization layer manages I/O requests from the server and then converts them to the correct physical disk.
The virtual storage model reduces hardware overhead by separating the operating system from physical devices and by providing one point of administration. It also allows for scalability by automatically adapting the physical capacity to meet the demands. It also lets administrators accomplish a variety of tasks in a non-disruptive fashion for example, moving data from over-utilized devices. This is accomplished by the technique of data migration. Generally, the mapping granularity determines how fast the meta-data can be updated, how much extra space is required during the migration and how fast the previous location can be marked as free.
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