Apple Xsan 1.1 - Manual (Page 16)

16 Chapter 1 Overview of Xsan
Fibre Channel Multipathing
Xsan can take advantage of multiple Fibre Channel connections between clients and
storage. Xsan can alternate between connections for each read and write, or assign
each LUN in a volume to one of the connections when the volume is mounted.
How Xsan Storage Is Organized
Users use 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 the
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.
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