Apple Xsan 1.0 - Manual (Page 21)

Chapter 2 Before You Begin 21
Xserve RAID supports all popular RAID levels. Each RAID scheme offers a different
balance of performance, data protection, and storage efficiency, as summarized in the
following table.
RAID 10, 30, and 50 schemes assume the use of AppleRAID software striping and aren’t
appropriate for use with Xsan, which performs its own striping. For more help choosing
RAID schemes for your arrays, see the Xserve RAID User’s Guide or the Xserve RAID
Technology Overview (at www.apple.com).
Deciding on the Number of Volumes
A volume is the largest unit of shared storage in the SAN. If your users need shared
access to files, you should store those files on the same volume. This makes it
unnecessary for them to pass copies of the files among themselves.
On the other hand, if security is critical, one way to control client access is to create
separate volumes and mount only the authorized volume on each client.
For a more typical balance of security and shared access, a flexible compromise is to
create a single volume and use folder access privileges to control access.
Note: The maximum size of any volume is 16 TB. If you need more than 16 TB of
storage, you need to create more than one volume.
Deciding How to Organize a Volume
You can help users organize data on a volume or restrict users to specific areas of the
volume by creating predefined folders. You can control access to these folders by
assigning access permissions using Xsan Admin.
You can assign folders to specific storage pools using affinities. You can, for example,
create a folder for data that requires fast access and assign that folder to your fastest
storage pool.
Assigning LUNs to Storage Pools
You should set up a storage pool using LUNs that have similar capacity and
performance characteristics.
RAID level Storage efficiency Read performance Write performance Data redundancy
RAID 0 Highest Very High Highest No
RAID 1 Low High Medium Yes
RAID 3 High to very high Medium Medium Yes
RAID 5 High to very high High High Yes
RAID 0+1 Low High High Yes
LL2652.book Page 21 Wednesday, July 28, 2004 3:45 PM