Overview of Storage Manager for SANs
Applies To: Windows Server 2003 R2
You can use Storage Manager for SANs to create and manage logical unit numbers (LUNs) on both Fibre Channel and iSCSI disk storage subsystems that support Virtual Disk Service (VDS).
Because of hardware, protocol, and security differences, LUN configuration and management on Fibre Channel and iSCSI environments is different. This section explains those differences, lists the types of LUNs that can be created, and defines LUNs in the context of partitions and volumes.
Managing LUNs in a Fibre Channel environment
In a Fibre Channel environment, LUNs created on a disk storage subsystem are assigned directly to a server or cluster, which accesses the LUN through one or more Fibre Channel host bus adapter (HBA) ports. You only need to identify the server or cluster that will access the LUN, and then select which HBA ports on that server or cluster will be used for LUN traffic.
When a server or cluster is identified, Storage Manager for SANs automatically discovers the available Fibre Channel HBA ports on that server or cluster. You can also add ports manually by typing their World Wide Name (WWN).
Managing LUNs in an iSCSI environment
Unlike in a Fibre Channel environment, LUNs created on an iSCSI disk storage subsystem are not only assigned to a server or cluster. For iSCSI, LUNs are first assigned to logical entities called targets.
Targets are created in order to manage the connections between an iSCSI device and the servers that need to access it. A target defines the portals (IP addresses) that can be used to connect to the iSCSI device, as well as the security settings (if any) that the iSCSI device requires in order to authenticate the servers that are requesting access to its resources.
Note
In most cases, you can create and manage targets yourself. However, some iSCSI storage subsystems only support simple target configurations, where targets are automatically created when you create a LUN. With simple target configurations, you also cannot delete a target or manually assign LUNs to it. LUNs are automatically assigned when they are created. For this type of subsystem, you just need to identify the server or cluster that will access the LUN, and the iSCSI subsystem will enable access from that server or cluster to the LUN.
To connect to a target, a server in the storage area network (SAN) uses an iSCSI initiator. An iSCSI initiator is a logical entity that enables the server to communicate with the target. The iSCSI initiator first logs on to the target, and only after access is granted by the target, the server can start reading and writing to LUNs assigned to that target. Each iSCSI initiator can have one or more network adapters through which communication is established.
As with Fibre Channel environments, you only need to identify the server or cluster that will access the LUN, and Storage Manager for SANs automatically discovers the iSCSI initiators on that server or cluster, and lists all the available adapters for those initiators. After the iSCSI initiator adapters have been discovered, you can select which adapters will be used for LUN traffic.
For more information, see Microsoft Storage Technologies - iSCSI at the Microsoft Web site.
Types of LUNs
Storage Manager for SANs supports the following types of LUNs.
| 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 |
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. |
LUNs, partitions and volumes
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.
After a LUN has been assigned to a server, you can create one or more partitions on that LUN. Partitions define how much physical space is allocated for storage. For the operating system to start writing and reading data on partitions, you need to create volumes by formatting the partitions using a file system. Volumes define how much logical space is allocated for storage. They can expand over more than one partition.