Overview of LUN Types
Applies To: Windows Server 2008
A LUN is a logical reference to a portion of a storage subsystem. A LUN can comprise a disk, a section of a disk, a whole disk array, or a section of a disk array in the subsystem. This logical reference, when it is assigned to a server in your SAN, acts as a physical disk drive that the server can read and write to. Using LUNs simplifies the management of storage resources in your SAN, because they serve as logical identifiers through which you can assign access and control privileges.
Types of LUNs
The LUN type determines performance and reliability characteristics of the LUN. You can use any LUN type that is supported by your storage subsystem.
| LUN type | Description |
|---|---|
Simple |
Simple LUNs use only one physical drive or one portion of a physical drive. This is the most basic type of LUN. |
Spanned |
Spanned LUNs are simple LUNs that span multiple physical drives. |
Striped |
Striped LUNs write data across multiple physical drives. Data is divided into blocks and spread among all the drives. Since striping writes data to all disks at the same rate, it provides increased I/O performance by distributing I/O requests across disks. Striped LUNs cannot be extended or mirrored, and do not offer fault tolerance. If one of the disks containing a striped LUN fails, the entire LUN fails. Select this type of LUN when improved I/O performance is required. |
Mirrored |
Mirrored LUNs are fault-tolerant LUNs that provide data redundancy by creating identical copies of the LUN on two physical drives. All read and write operations happen concurrently on both drives. If one of the physical disks fails, the data on the failed disk becomes unavailable, but the LUN continues to be available using the unaffected disk. Select this type of LUN when fault tolerance is required. |
Striped with Parity (RAID-5) |
Striped LUNs with parity are fault-tolerant LUNs with data and parity spread intermittently across three or more physical disks. If a portion of a physical disk fails, the data that was on the failed portion is recreated from the remaining data and parity information. This type of LUN provides better read performance than a mirrored LUN, but write performance is reduced by the parity calculation. Select this type of LUN when fault tolerance is required and improved read performance is desired. |
Volumes on LUNs
After a LUN has been assigned to a server, it will be listed as a disk in that server and you will be able to create one or more volumes on the disk. The performance and reliability characteristics of all volumes that are created on the disk will be determined by the LUN type.