HP Surestore NAS - Manual (Page 14)

14
hard disks, depending on your storage needs. Drive capacities may be mixed. If drive speeds
are mixed, system performance will approximate the lowest speed drive in use.
Virtual Array
Your HP Virtual Array is preconfigured for you at installation by the HP Customer Engineer.
Administrators with a strong working knowledge in HP -UX administration and the Logical Volume
Manager can make changes through the Command View SDM. The term “Virtual Array” refers
to the way the disks within the array are treated as a pool of data storage blocks instead of real
physical disks. Further information on your VA is available in the Virtual Array section of this
manual.
Active Spare
The active spare feature in the storage array offers increased protection against disk failure. An
active spare ensures that the array can restore data redundancy and performance as quickly as
possible following a hard disk failure.
Active spare reserves capacity to perform a rebuild in the event of a disk failure. If you are using
disks of different capacities in your array, active spare reserves enough space to rebuild the
largest disk. As with logical volumes, the capacity reserved for the active spare is distributed
across all the disks in the array; no one physical disk contains the active spare.
Active spare is similar to the dedicated hot spare disks used in some conventional arrays.
However, those arrays let the hot spare remain idle until it is needed. This array uses the active
spare for RAID 1+0 storage until the spare is needed. This provides the added benefit of
enhancing performance while also protecting against disk failure.
Logical Storage
Logical Unit Number
Logical unit numbers (LUNs) prepare the physical disk space for use.
A logical unit number (LUN) is a unique identifier to differentiate between separate devices (each
of which is a logical unit). Each LUN is a unique number that identifies a specific unit of storage.
The number of LUNs supported on your NAS VA is dependent on the array hardware installed in
your solution. The VA 7400 array can support up to 1024 LUNs. The VA 7100 array can support
up to 128 LUNs. Typically, your NAS VA solution will use only a very small number of LUNs.
Volume Groups
Volume groups combine the space from LUNs and make the space accessible to the file system
for creating logical volumes and directories, which can then be made accessible to users.
A volume group is a collection of between 1 and 32 LUNs. A LUN may belong to only one volume
group per system. Each system can contain as many as 255 volume groups. When a LUN is
assigned to a volume group, the volume's physical blocks of storage media are organized into
physical partitions of a size you specify when you create the volume group.
Logical Volumes
A logical volume is a section of disk space that holds computer data. A large volume group can
be divided into several logical volumes or partitions, each of which is treated as a separate disk.
Logical volumes are the basic unit of logical storage for a file system on the HP NAS VA. Logical
volumes can be further subdivided into individual directories.