Apple Xsan 1.4 - Manual (Page 49)

Chapter 2 Setting Up a Storage Area Network 49
Combining Clients and Controllers
The same computer can function as both a metadata controller and a client. It’s
possible, for example, to set up a SAN consisting of a single Xserve RAID and one
computer that acts as both controller and client. Any computer you specify as a
controller can also act as a client.
If, for example, you don’t have a computer to dedicate as a standby controller, you can
assign a computer that is normally used as a client to take over controller duties if the
primary controller fails.
To keep clients and controllers separate, you can set up client-only computers for your
users.
Choosing Where to Store Metadata and Journal Data
The metadata and journal data that describe a volume are not stored on the volume’s
metadata controller but on the volume itself. By default, they are stored on the first
storage pool in the volume. If the volume consists of more than one storage pool,
you can choose which storage pool is used to store metadata and journal data.
In most cases, storing metadata and journal data on the same storage pool as user
data results in adequate performance. However, for the best possible performance,
store metadata and journal data on a separate storage pool within the volume and
make sure that the LUNs used are connected to a different RAID controller than the
LUNs that make up user data storage pools.