Storage Management Overview
55
NAS 4000s and 9000s Administration Guide
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.
After the physical drives are grouped into arrays, they are ready to be converted into logical
drives. Options for working with arrays vary from SAN storage to SAN storage system. The
individual documentation included with each storage system should be reviewed.
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. See the section “Dynamic
Growth” in chapter 4 for additional information on LUN extension and use by the operating
system.
Figure 27: 2 arrays (A1, A2) and 5 logical drives (L1 through L5) spread over 5 physical drives
Note:
This type of configuration may not apply to all supported SANs and serves only as an
example.
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.
L4
L5
L3
A1
L1
L2
A2
Summary of Contents for NAS 4000s
Page 18: ...About this Guide 18 NAS 4000s and 9000s Administration Guide ...
Page 92: ...Disk Management 92 NAS 4000s and 9000s Administration Guide ...
Page 196: ...NetWare File System Management 196 NAS 4000s and 9000s Administration Guide ...
Page 246: ...Index 246 NAS 4000s and 9000s Administration Guide ...
