Apple Xsan 1.x - Manual (Page 29)

Chapter 3 Deployment Examples 29
In a NAS configuration, the real clients of the storage are not connected to the SAN,
but instead connect to the storage server over a TCP/IP network. The storage server
itself is the true Xsan client computer and, in the case of a single server computer, is
also the SAN controller. The server provides file services using Mac OS X Server AFP,
SMB, or NFS services to other computers on the network.
Objectives of This Configuration
This example shows one way to set up a SAN to meet the following requirements:
 Provide 100 GB of network-accessible storage for each of 80 users
 Support users running Mac OS X, Windows, or UNIX
 Storage must be always available
Deployment Decisions
The following paragraphs answer the planning questions listed in the Xsan
Administrator’s Guide in a way that satisfies the objectives of the network attached
storage deployment example.
How much storage is needed?
100GB of storage for each of 80 users requires at least 8 TB of user disk space. An Xserve
RAID with a full 14 400 GB drive modules can provide approximately 5.6 TB of total
storage. However, to provide redundancy, we’ll set aside one drive on each controller
(on each half of an Xserve RAID system) as a spare, and organize the remaining 6 drives
as RAID 5 arrays. Using RAID 5 means that the equivalent of one drive (distributed
across all 6 drives) out of each array is dedicated to RAID parity. So, each array on each
Xserve RAID controller has the equivalent of 5 drives available to store 2 TB of user files,
or a total of 4 TB per Xserve RAID. At 100 GB per user, each Xserve RAID can support
40 users. Three Xserve RAID systems, configured as RAID 5 arrays with one spare
drive per unit, will provide sufficient space and leave an extra array for metadata and
journal data.
What storage arrangement makes the most sense for user workflow?
In this example, users don’t connect to the SAN directly, so they don’t see how storage
in the SAN is organized. Instead, they connect to share points offered by file services on
the file servers. The true Xsan clients are the file servers themselves. The intent of the
NAS configuration is to offer large amounts of storage without imposing any particular
organization (users can do that themselves), so it suffices to set up large volumes with
a top-level folder for each user.
How is the storage presented to users?
When users connect to the server share point, they see a list of folders, one for each
user.