A storage volume is an identifiable unit of data storage. It can be a removable hard disk, but it does not have to be a unit that can be physically removed from a computer or storage system.
Storage volume vs. partition
Each storage volume has a system-unique name or number that allows a user to identify it. In some systems, the physical unit may be divided into several identifiable volumes.
The main difference between a storage volume and partition is the type of disk used. A volume is created on a dynamic disk -- a logical structure that can span multiple physical disks -- while a partition is created on a basic disk.
A volume is also more flexible than a partition. Storage volumes can expand or contract, and they use mirroring and striping. On a physical server, the OS is typically installed on a partition, while everything else is installed on a volume. In addition, volumes support multiple disks that can be organized into various RAID structures that protect stored data in the event of a hardware failure.
Virtual machines often use partitions because they are easy to create, but some virtualization-aware backup software applications do not support the use of storage volumes and dynamic disks inside of a VM. In those cases, volumes can still be used, just at the host level.
Logical volumes and management
Logical volume management is a form of storage virtualization that offers a more flexible approach to managing disk storage space than traditional partitioning. Using this approach, a storage administrator can partition the capacity of disk drives on an array and pool them instead of allocating all disk storage space at initial setup.
Storage volumes may be defined for various user groups within the enterprise. New storage can be added to a particular group without requiring user files to be redistributed, making the most efficient use of space. When old drives are retired, the data they contain can be transitioned to new drives -- ideally without disrupting service.
A volume manager is software within an OS that controls capacity allocation for storage arrays, and it can help with performance. Most OSes provide an option for managing volume.
Volumes are often confused with logical unit numbers (LUNs). A LUN is the identifier name for a logical volume and is the logical abstraction between a physical drive or volume and applications.
A major drawback to placing large numbers of files onto a single volume is that large volumes take longer to back up. Users also have to consider the amount of damage that will occur from a volume-level failure. Most multidisk volumes have built-in redundancy to prevent the storage volume from failing in the event of a hard disk failure.