56 Planning: MD3600f Series Storage Array Terms and ConceptsYou can manually configure a host server-to-virtual disk mapping. When youconfigure host server-to-virtual disk mapping, consider these guidelines:• You can define one host server-to-virtual disk mapping for each virtual diskin the storage array.• Host server-to-virtual disk mappings are shared between RAID controllermodules in the storage array.• A unique LUN must be used by a host group or host server to access avirtual disk.• Not every operating system has the same number of LUNs available for use.Host TypesA host server is a server that accesses a storage array. Host servers are mappedto the virtual disks. Host servers have the following attributes:• Host name—A name that uniquely identifies the host server.• Host group (used in Cluster solutions only)—Two or more host serversassociated together to share access to the same virtual disks.This host group is a logical entity you can create in MDSM. All host serversin a host group must be running the same operating system.• Host type—The operating system running on the host server.Snapshot Virtual DisksA snapshot is a point-in-time image of a virtual disk. The snapshot providesan image of the virtual disk at the time the snapshot was created. You create asnapshot so that an application (for example, a backup application) canaccess the snapshot and read the data while the source virtual disk remainsonline and user-accessible. When the backup is completed, the snapshotvirtual disk is no longer needed. You can create up to four snapshots pervirtual disk.Snapshots are used to recover previous versions of files that have changedsince the snapshot was taken. Snapshots are implemented using a copy-on-write algorithm, which makes a backup copy of data the instant an erroroccurs. Data on a virtual disk is copied to the snapshot repository before it ismodified. Snapshots can be created instantaneously or can be scheduled andtake up less overhead than a full physical copy process.
