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3.1.2. Logical Storage Element
Logical storage elements consist of those components that translate the
physical storage elements to file system elements. The storage server uses
the Window Disk Management utility to manage the various types of disks
presented to the file system. There are two types of LUN presentation: basic
disk and dynamic disk. Each of these types of disk has special features that
enable different types of management.
Logical Drives (LUNs)
3.1.2.1.
While an array is a physical grouping of hard drives, a logical drive consists
of components that translate physical storage elements into file system
elements. 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.
Through the use of basic disks, primary partitions or extended partitions can
be created. Partitions can only encompass one LUN. Through the use of
dynamic disks, volumes can be created that span multiple LUNs. The
Windows Disk Management utility can be used to convert disks to dynamic
and back to basic, and manage the volumes residing on dynamic disks.
Other options include the ability to delete, extend, mirror, and repair these
elements.
Partitions
3.1.2.2.
Partitions exist as either primary partitions or extended partitions and can be
composed of only one basic disk no larger than 2 TB. Basic disks can also
only contain up to four primary partitions, or three primary partitions and one
extended partition. In addition, the partitions on them cannot be extended
beyond the limits of a single LUN. Extended partitions allow the user to
create multiple logical drives. These partitions or logical disks can be
assigned drive letters or be used as mount points on existing disks. If mount
points are used, it should be noted that Services for UNIX (SFU) does not
support mount points at this time. The use of mount points in conjunction
with NFS shares is not supported.
Volumes
3.1.2.3.
When planning dynamic disks and volumes, there is a limit to the amount of
growth a single volume can undergo. Volumes are limited in size and can
have no more than 32 separate LUNs, with each LUN not exceeding 2
terabytes (TB), and volumes totaling no more than 64 TB of disk space.
The RAID level of the LUNs included in a volume must be considered. All of
the units that make up a volume should have the same high-availability
characteristics. In other words, the units should all be of the same RAID
level. For example, it would not be a good practice to include both a RAID
0+1 and a RAID 5 array in the same volume set. By keeping all the units the
same, the entire volume retains the same performance and high-availability
characteristics, making managing and maintaining the volume much easier.
If a dynamic disk goes offline, the entire volume dependent on the one or
more dynamic disks is unavailable. There could be a potential for data loss
depending on the nature of the failed LUN.
3-3
Tandberg Viking Series Storage Server Administration Manual
Storage & File Server Management
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