Apple Xsan 2 (Third Edition) - Manual (Page 28)

Choose a different primary metadata controller for each volume, and set up volume Â
failover priorities to minimize the possibility of more than one volume failing over to
the same metadata controller.
If all computers on your SAN are running Xsan 2.2, enable Extended Attributes for
Â
your volumes to eliminate the overhead of file information being stored in multiple
hidden files.
Availability Considerations
If high availability is important for your data, set up at least one standby metadata
controller in addition to your primary metadata controller. Also, consider setting up
dual Fibre Channel connections between each client, metadata controller, and storage
device using redundant Fibre Channel switches.
WARNING: Losing a metadata controller without a standby can result in the loss of
all data on a volume. A standby controller is strongly recommended.
Security Considerations
If your SAN supports projects that must be secure and isolated from each other, create
separate volumes for each project to eliminate any possibility of the wrong client or
user accessing files stored on a volume.
As the SAN administrator, you control which client computers can use a volume.
Clients can’t browse for or mount SAN volumes on their own. You use Xsan Admin to
unmount a volume on clients that shouldn’t have access to it.
You can also set up access control lists (ACLs) in Xsan Admin or assign user and group
permissions to folders using standard file access permissions in the Finder.
Choosing RAID Schemes for LUNs
Much of the reliability and recoverability of data on a SAN is provided not by Xsan, but
by the RAID arrays you combine to create your storage pools and volumes. Before you
set up a SAN, you use the RAID system configuration or administration application to
prepare LUNs based on specific RAID schemes.
WARNING: If a LUN belonging to an Xsan volume fails and can’t be recovered, all
data on the volume is lost. It is strongly recommended that you use only redundant
LUNs (LUNs based on RAID schemes other than RAID 0) to create Xsan volumes.
LUNs configured as RAID 0 arrays (striping only) or LUNs based on single drives are
difficult or impossible to recover if they fail. Unprotected LUNs such as these should
be used only in storage pools that store scratch files or other data that you can afford
to lose.
28 Chapter 2 Planning a Storage Area Network