Apple Xsan 2 - Manual (Page 51)

Chapter 3 Plan a SAN 51
Estimate 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 require approximately 10 GB of metadata on the volume’s
metadata storage pool.
The journal requires between 64 KB and 512 MB. Xsan configures a fixed size when you
create a volume. Due to the small size, you can use a single RAID 1 LUN for the journal
storage pool. To maximize the performance benefit of a separate journal storage pool,
dedicate entire physical disks to the RAID 1 LUN.
Choose an allocation strategy
If you choose a preset volume type when you set up a volume, Xsan Admin sets its
volume allocation strategy for you. Later, you can change the allocation strategy by
editing volume settings with Xsan Admin.
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, or balance:
 If you choose round robin, Xsan writes data to each storage pool in the volume in
turn. This is normally the best choice for performance.
 If you choose fill, Xsan writes data to the first storage pool in the volume until that
storage pool is full, and then moves to the next storage pool. This is a good choice
to keep a specific storage pool unused as long as possible.
 If you choose balance, Xsan writes data to the storage pool that has the most free space.
Plan the Ethernet TCP/IP network
Ethernet connections are used in several ways in an Xsan SAN:
Xsan clients and metadata controllers use Ethernet to exchange volume metadata. Â
Xsan clients can use Ethernet for access to networks outside the SAN (campus or Â
corporate intranet or the Internet).
Xsan metadata controllers can use Ethernet connections for remote management.
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RAID systems can use Ethernet connections for system management. Â
Fibre Channel switches can use Ethernet connections for switch management. Â
You have two options:
Use one Ethernet network for all traffic. This is the less expensive option, but is also Â
less secure and might not provide the best performance.
Use two separate networks—one for metadata and another for all other IP traffic.
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This configuration is slightly more expensive (requiring two Ethernet adapters for
each computer and an additional switch) but offers greater security and better
performance because routine network traffic doesn’t interfere with SAN volume
metadata traffic.