Apple Xsan 1.0 - Manual (Page 13)

Chapter 1 Overview of Xsan 13
One of your first tasks when you set up a SAN volume is to prepare LUNs. If the two
RAID 5 arrays on a new Xserve RAID are not right for your application, you can use RAID
Admin to create arrays based on other RAID schemes. For help choosing schemes for
your LUNs, see “Choosing RAID Schemes for LUNs” on page 23.
The illustration on page 12 shows four Xserve RAID systems hosting two arrays each.
Half of the arrays use a RAID 0 scheme (striping only) for speed while the others use
RAID 5 (distributed parity) to ensure against data loss. Xsan sees the arrays as LUNs that
can be combined to create a volume.
After your Xserve RAID LUNs are set up, you label and initialize them for use with the
Xsan file system using Xsan Admin.
Storage Pools
LUNs are combined to form storage pools. A storage pool in a small volume might
consist of a single RAID array, but storage pools in many volumes consist of multiple
arrays.
Xsan distributes file data in parallel across the LUNs in a storage pool using a RAID 0
(striping) scheme. So, you can improve access speed by distributing available storage
over several LUNs in a storage pool.
You can set up storage pools that have different performance or recoverability
characteristics and assign folders to them using affinities. Users can then select where
to store files based on their need for speed or safety. See “Folders With Affinities” on
page 14.
As an example, the illustration on page 12 shows eight LUNs combined into two
storage pools, one pool consisting of RAID 0 (fast but not recoverable) arrays and the
other made up of RAID 5 (not as fast, but recoverable) arrays. Xsan stripes data across
the four LUNs in each storage pool.
You use Xsan Admin to add available LUNs to specific storage pools.
Volumes
Storage pools are combined to create the volumes that users see. From the user’s
perspective, the SAN volume looks and behaves just like a large local disk, except that:
• The size of the volume can grow as you add underlying arrays or storage pools
• Other users on the SAN can access files on the volume at the same time
In the example illustrated on page 12, two storage pools are combined to create a
single shared volume.
You create volumes and mount them on client computers using the Xsan Admin
application.
LL0192.book Page 13 Thursday, July 29, 2004 5:20 PM