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often mask its use under other names due to ATM s failure to
achieve marketing buzz. Many more carrier services are ATM-based
than users realize. For example, AT&T s IP-enabled Frame Relay is
a service that attaches special labels representing groups of user IP
addresses to create the illusion of an IP virtual private network
(VPN) it is really ATM between AT&T switches. SBC s Project
Pronto is sold as a DSL connection to a nearby neighborhood gate-
way, but it is all ATM from there. Sprint s Integrated On-Demand
Network (ION) is pure ATM from the customer premises device out.
Standards groups are working on ways to make ATM more attrac-
tive in LANs. Multiprotocol over ATM (MPoA) standards let non-
ATM networks send traffic across an ATM network and tap into
ATM QoS guarantees. ATM also has gained more flexibility in the
WAN via recent standards. Some ATM carriers now allow users who
cannot afford T-3 connections to choose multiples of T-1 bit rates via
inverse multiplexing over ATM. And all the large carriers now allow
users to keep Frame Relay equipment at some sites and ATM equip-
ment at other sites in a single corporate network. This occurs via a
standard called Frame Relay-to-ATM Interworking.
Few users will ever realize ATM s early promise of sending all
types of traffic over a single network. This is so because ATM took
too long to overcome early problems with expensive, hard-to-use
equipment, and meanwhile, most efforts to create a single global
network shifted to IP. ATM remains a key consideration for users
needing to reduce disparate networks today while still enjoying reli-
able CoSs for different kinds of traffic.
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Configuring SANs: Dos and Don ts
Chapter 4
76
Summary
SANs are growing rapidly because they solve problems. The problem
is manageability of large and ever-increasing amounts of disk stor-
age. When storage is attached directly to the computer through high-
speed cable, the storage device can meet the needs of that computer
very well. When computers are networked together, each computer
with its own attached storage, total storage resource management is
difficult or impossible to achieve.
The SAN approach offers many storage management advantages,
including the ability to
% Share a pool of storage.
% Easily grow the size of the storage pool.
% Balance the load to each physical device.
% Eliminate downtime.
% Easily share backup devices.
% Back up without degrading performance for the network users.
% Manage storage resource easily and efficiently.
% Manage computing resource separately from storage resource.
The storage of digital data most of us take for granted as a kind of
technological achievement that occurs independent of our recogni-
tion and operates solely as a behind-the-scenes process. Within the
last 10 years, the Internet has grown from thousands of users to mil-
lions (53.5 million in 2001). SAN developments have increased the
speed, reliability, and capacity of mass storage technologies, making
it possible to save limitless quantities of information. The connec-
tions through which these systems exchange data do not always
transmit mass quantities of information well.
Of the over 70 percent of mission-critical data stored on main-
frames, the SAN community has all but ignored legacy systems. The
clients, or end users, work from their workstations where stored data
are backed up over the LAN. The LAN maintains UNIX, WINNT,
Netware, or other legacy system servers types. Islands of SCSI disks
process and provide first-level storage of data that are then backed
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Configuring SANs: Dos and Don ts
Configuring SANs: Dos and Don'ts
77
up to a tape library system. LAN-free backups enable a SAN to share
one of the most expensive components of the backup and recovery
system, the tape or optical library and the drives within it.
The methodology shown in Figure 4-2 worked as long as a LAN
could support network traffic and backups. Even with a state-of-the-
art LAN, you will encounter individual backup clients that are too
big to back up enterprise-wide across the LAN. Prior to building a
SAN, you need to analyze your system requirements. Develop a SAN
architecture that meets your system requirements and analysis.
SAN architecture development will require good management in
recognizing performance considerations in collecting data and
implementing phase cycle development procedures successfully.
In Chapter 5, Fibre Channel, we delve extensively into Fibre
Channel and its products and cabling issues.
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