Logical Drives (Luns) - HP 345646-001 - StorageWorks NAS 2000s External Storage Server Administration Manual

Logical Drives (LUNs)

As previously stated, drive array technology distributes data across a series of individual hard
drives to unite these physical drives into one or more higher performance arrays. Distributing
the data allows for concurrent access from multiple drives in the array, yielding faster I/O rates
than non arrayed drives.
While an array is a physical grouping of hard drives, a logical drive is the configuration of the
arrays that is presented to the operating system.
When planning to allocate space on the NAS device, consider that the maximum number of
LUNs in a dynamic disk is 32 and the largest single LUN that can be utilized by the operating
system is 2 TB. It should also be noted that the largest basic disk that can exist is 2 TB and the
largest volume that can exist is 64 TB. Format of the partition or volume impacts the largest
file system that can exist as well.
HP recommends creating one logical drive from the array. After the physical drives are
grouped into arrays, they are ready to be converted into logical drives.
It is important to note that a LUN may extend over (span) all physical drives within a storage
controller subsystem, but cannot span multiple storage controller subsystems.
After a LUN has been created, it is possible to extend the size, either through the HP Array
Configuration Utility or via Disk Management. See chapter 4 for additional information.
Note:
L1
L2
Figure 23: 2 arrays (A1, A2) and 5 logical drives (L1 through L5) spread over 5 physical drives
Drive failure, although rare, is potentially catastrophic. For example, in the previous figure
using simple striping, failure of any hard drive will lead to failure of all logical drives in the
same array, and hence to data loss.
To protect against data loss from hard drive failure, arrays should be configured with fault
tolerance. Several fault tolerance methods have been devised and are described in the
following sections.
NAS 2000s Administration Guide
After a LUN has been extended, you must go into Disk Manager to allocate that space.
A1
Storage Management Overview
A2
L3
L4
L5
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