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 “Choosing RAID Schemes for LUNs” on page 28.
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Chapter 1
Overview of Xsan
Chapter 1
Overview of Xsan
17
The illustration on page 16 shows eight LUNs. The LUN that stores metadata and
journal information uses RAID level 1 (mirrored) to prevent metadata loss. One LUN
stores users’ data on a RAID 0 array (striping only) for best speed and storage efficiency
but no data protection. The other data LUNs use RAID 5 (distributed parity) for high
performance and storage efficiency with data protection. Xsan sees the RAID arrays as
LUNs that can be combined to create a volume.
Your RAID LUNs are labeled and initialized for use with the Xsan file system when you
use Xsan Admin to set up a volume.