56 Planning: MD3600f Series Storage Array Terms and Concepts
You can manually configure a host server-to-virtual disk mapping. When you
configure host server-to-virtual disk mapping, consider these guidelines:
• You can define one host server-to-virtual disk mapping for each virtual disk
in the storage array.
• Host server-to-virtual disk mappings are shared between RAID controller
modules in the storage array.
• A unique LUN must be used by a host group or host server to access a
virtual disk.
• Not every operating system has the same number of LUNs available for use.
Host Types
A host server is a server that accesses a storage array. Host servers are mapped
to 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 servers
associated together to share access to the same virtual disks.
This host group is a logical entity you can create in MDSM. All host servers
in a host group must be running the same operating system.
• Host type—The operating system running on the host server.
Snapshot Virtual Disks
A snapshot is a point-in-time image of a virtual disk. The snapshot provides
an image of the virtual disk at the time the snapshot was created. You create a
snapshot so that an application (for example, a backup application) can
access the snapshot and read the data while the source virtual disk remains
online and user-accessible. When the backup is completed, the snapshot
virtual disk is no longer needed. You can create up to four snapshots per
virtual disk.
Snapshots are used to recover previous versions of files that have changed
since the snapshot was taken. Snapshots are implemented using a copy-on-
write algorithm, which makes a backup copy of data the instant an error
occurs. Data on a virtual disk is copied to the snapshot repository before it is
modified. Snapshots can be created instantaneously or can be scheduled and
take up less overhead than a full physical copy process.
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