Apple Xsan 1.1 - Manual (Page 31)

Chapter 2 Setting Up a Storage Area Network 31
Important: If you’re using a version of Xsan earlier than 1.1, be sure to store metadata
and journal data only on the first or the first and second storage pools in the volume.
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 separate storage pools 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.
Estimating Metadata and Journal Data Storage Needs
To estimate the amount of space required for Xsan volume metadata, assume that 10
million files on a volume will require approximately 10 gigabytes of metadata on the
volume’s metadata storage pool.
Choosing an Allocation Strategy
The allocation strategy you choose for a volume determines the order in which its
storage pools are filled with data. You can choose round robin, fill, and balance.
If you choose round robin, Xsan writes new data in turn to each storage pool in the
volume.
If you choose fill, Xsan writes all new data to the first storage pool in the volume until
that storage pool is full, then moves to the next storage pool. This is a good choice if
you want to keep a particular storage pool unused as long as possible.
If you choose balance, Xsan writes new data to the storage pool with the most free
space.
Connecting Computers and Storage Devices
Before you set up your Xsan SAN, connect client computers, controller computers, and
storage devices to the SAN’s Fibre Channel and Ethernet networks. Make sure your
networks meet the requirements summarized under “Fibre Channel Fabric” on page 22
and “Ethernet TCP/IP Network” on page 23.
Preparing LUNs (RAID Arrays and Slices)
Xserve RAID systems usually come preconfigured with two RAID 5 arrays, one on each
side (on each controller). So, out of the box, each Xserve RAID provides two LUNs. If this
suits your needs, no other preparation is needed.
If you want to set up some other combination of RAID arrays or slices, you need to do
so using the RAID Admin utility before you can add the resulting LUNs to your SAN’s
storage pools. For help using RAID Admin, see Using RAID Admin 1.2 and Disk Utility
(available at www.apple.com/server/documentation). For information on choosing a
RAID scheme, see “Choosing RAID Schemes for LUNs” on page 28.