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How xsan storage is organized, Luns, 34 how xsan storage is organized 34 – Apple Xsan 2 User Manual

Page 34

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How Xsan storage is organized

Although an Xsan volume mounted on a client computer looks like a single disk, it
consists of multiple physical disks combined on several levels using RAID techniques.

The following illustration shows an example of how disk space provided by drive
modules in several RAID systems is combined into a volume that users see as a large
local disk.

RAID Arrays
(LUNs)

Data striping
across LUNs

Storage pools

Affinity tags

Folder affinities

SAN volume

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The following paragraphs describe these elements and how you combine them to
create shared Xsan volumes.

LUNs

The smallest storage element you work with in Xsan is a logical storage device called a
SCSI logical unit number, or LUN. A LUN represents a group of drives combined into a
RAID array.

You create a LUN when you create a RAID array on a RAID storage device. The RAID
system combines physical drives into an array based on the RAID scheme you choose.
Each array appears on the Fiber Channel network as a LUN.

If the standard RAID arrays on your RAID systems aren’t right for your application, you
can use the RAID system management software to recreate arrays based on other
RAID schemes or different numbers of drive modules. For information about other
RAID schemes, see “Choose RAID schemes for LUNs” on page 47.

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Chapter 2

Overview of Xsan