Apple Xsan 1.0 - Manual (Page 10)

10 Chapter 1 Introduction to Xsan
How Xsan Storage Is Organized
Users work with an Xsan volume the same way they use a local disk. What they don’t
see is that the SAN volume actually consists of numerous physical disks combined on
several levels using RAID techniques.
The following illustration shows an example of how disk space provided by individual
drive modules in Xserve RAID systems is combined into a volume that users see as a
large local disk.
The following paragraphs describe these storage elements and how you organize them
to create shared Xsan volumes.
LUNs (RAID Arrays)
The smallest storage element you work with in Xsan is a logical storage device called a
LUN (a SCSI logical unit number). In most storage area networks, a LUN represents a
group of drives such as a RAID array or a JBOD (just a bunch of disks) device. In Xsan,
LUNs are Xserve RAID arrays or slices.
You create a LUN whenever you use RAID Admin to create an Xserve RAID array. The
controller hardware and software in the Xserve RAID system combine individual drive
modules into an array based on the RAID scheme you choose. Each array appears on
the Fibre Channel network as a LUN, and if you slice the array into two or more slices,
each slice appears as a separate LUN.
Faster
Safer
Storage pool Storage pool
(Striping) (Striping)
RAID 0
array
RAID 0
array
LUN LUN
RAID 0
array
RAID 0
array
LUN LUN
RAID 5
array
RAID 5
array
LUN LUN
RAID 5
array
RAID 5
array
LUN LUN
Shared SAN
volume
Affinity Affinity
LL2652.book Page 10 Wednesday, July 28, 2004 3:45 PM