Defining the Technologies
To understand how and
when to use technologies such as NAS or SAN, it is important to
understand what they are and what they offer. The technologies differ in
how they are used and what advantages they provide. Many administrators
assume that they need a SAN when often a NAS will suffice. Because
information technology (IT) budgets are far from limitless, it is to
your advantage to know that you aren’t overbuying for your solution. By
the same token, it is often less expensive to buy your solution all at
once rather than trying to expand it later.
What Is a SAN?
A SAN is a high-speed,
special-purpose network or subnetwork that connects various data storage
devices with associated data servers on behalf of a larger network of
users. Typically, a SAN is but part of an overall network of computing
resources for an enterprise. A SAN is usually located in relative
proximity to other computing resources such as databases and file
servers but might also extend to remote locations for backup and
archival storage. These remote locations are traditionally connected via
wide area network (WAN) carrier technologies, such as asynchronous
transfer mode (ATM) or Synchronous Optical Networks (SONETs).
It is very important
to understand that the SAN is more than just the chassis that contains
the disks. It includes the redundant array of inexpensive or independent
disks or drives (RAID) controllers for the disks, the Fibre Channel
switching fabric, and the host bus adapters (HBAs) that reside in the
data servers. SANs are traditionally connected to hosts via Fibre
Channel and talk via Fibre Channel Protocol. Although it can be fairly
easy to support dual-arbitrated fiber loops in a corporate environment,
keep in mind that one of the primary benefits of SAN is the ability to
do block-level mirroring to another SAN. If this SAN is located
remotely, up to 1,000km away with current fiber technology, a company
needs to have fiber between the two locations. A fiber connection across
those kinds of distances can be quite expensive.
SAN technologies excel in
the area of disk performance. Fibre Channel networks regularly push
4Gb/sec of throughput. Although SCSI technologies can move data at up to
320Mb/sec and can be bonded together for higher throughput, they are
limited to less than
25 feet of distance. SAN, not unlike SCSI, is seen by the host system as
raw disk space. This is also referred to as a block-level technology.
In the past, database applications required block-level access to the
disk as well as the “near 0 latency” offered by SAN.
Tip
Although most SAN manufacturers refer to the performance of their products as having zero latency,
it is important not to misinterpret this. Zero latency refers to the
fact that Fibre Channel has extremely low overhead and doesn’t add
additional latency. The laws of physics, on the other hand, are still in
effect. A 1,000-km fiber run between remote locations still takes 7
milliseconds round-trip.
What Is NAS?
NAS is a hard disk
storage technology that uses an Ethernet connection rather than being
attached directly to the host computer that is serving applications or
data to a network’s users. By removing storage access and its management
from the host server, both application programming and files can be
served faster because they are not competing for the same processor
time. The NAS device is attached to a local area network (LAN) via
Ethernet and given an IP address. File requests are mapped by the host
server to the NAS device.
NAS consists of hard
disk storage, including multidisk RAID systems and software for
configuring and mapping file locations to the network-attached device.
NAS software can usually handle a number of network protocols, including
Microsoft’s Internetwork Packet Exchange, Common Internet File System,
and NetBEUI; Novell NetWare Internetwork Packet Exchange; and Sun
Microsystems Network File System. Configuration, including the setting
of user access priorities, is usually possible using a web browser
though many NAS offerings require command-line configuration. Most NAS
manufacturers include specialized software for allowing specific
applications such as Structured Query Language (SQL) or Exchange to take
advantage of special functions provided by the NAS. These functions
include things like mirroring, failover, automated recovery, and
snapshotting.
NAS has the
advantage of using existing Ethernet technologies that are much less
expensive than fiber technologies. With the availability of 10Gb
Ethernet, NAS is able to compete with Fibre Channel–based technologies
even with the added overhead of Ethernet over Fibre Channel. In most
scenarios, Gigabit Ethernet is sufficient for Exchange 2007 servers,
especially if multiple connections are employed.
When Is the Right Time to Implement NAS and SAN Devices?
There are many reasons to
implement a NAS or SAN solution in favor of direct attached storage. In
the case of Exchange 2007, if the requirements for storage
consolidation, reduction in mailbox server count, centralized management
of disk resources, service level agreement (SLA) recoverability times,
or near real-time mirroring of data justify the cost of
a SAN or NAS solution, it is time to explore those options. To make an
informed decision about when to make the switch within your Exchange
2007 environment, it is important for you to pass through several
phases:
Analyze—
Gather usage metrics and performance metrics. Determine how storage is
being used and how it affects the business processes. Determine if disk
throughput is the bottleneck in your Exchange deployment.
Plan—
Determine the current limitations of your storage solutions. Prioritize
the problems and determine if there is a better way. Don’t fall into
the trap of doing things just because they were always done a particular
way.
Develop—
Build the proposed solution for testing. Perform benchmarking to show
improvements over the old methods. Experiment with various functions of
Exchange 2007 on different types of disks. Get a feel for the
improvement versus the costs.
Pilot—
Test the solution and improve it based on user feedback. Educate the
user population on how to take full advantage of the new functions and
determine the improvements in efficiencies.
Deploy— Deliver the solution to the masses.
Following this
methodology not only streamlines the process of implementing new and
more efficient storage technologies, but also provides valuable data to
help upper management buy into the upgrades and support the storage
program for the Exchange environment.
Analyzing Your Storage Needs
The first phase of any good
project is an in-depth analysis of the environment and its needs. In
the case of storage systems, it is critical to identify any systems with
special requirements. This includes systems that require multiple
layers of redundancy, systems that are under extremely tight SLAs, and
systems that cannot tolerate a loss of data. In the case of Exchange
2007 that is deployed by role, it is most likely only the Mailbox server
role that will benefit significantly from using SAN or NAS
technologies. Similarly, you might determine that it is less expensive
to take advantage of the additional memory that can be used by Exchange
2007 because of its 64-bit architecture, to increase the caching of
database transactions and, therefore, reduce the necessary number of
disks. NAS and SAN solutions can be very expensive compared to
purchasing memory for a server.
Another key
area to understand is the capacity requirements of the enterprise. If an
investment is going to be made in storage, it is a good idea to plan
for several years of growth. Look at the number of servers in the
environment. If additional servers have been added simply because that
is the way things were always done, it is time to look at shifting the
philosophy to doing things because it is the right way to do it.
Tip
Disk drives get
larger, faster, and less expensive each year. When planning for the
future, keep expandability in mind. By buying a partially filled chassis
now and adding additional disks later, you can take advantage of
falling disk prices and save money over the long run and still get the
full capacity they need and the benefits of fewer chassis.
Planning the Storage Solution
Storage technologies can
be very confusing. In most situations, valid arguments can be made for
using any of the available technologies. This is a situation in which it
makes a lot of sense to get your vendors involved. Contact your
potential vendors and let them know what your storage requirements are.
Often, they have worked with other companies with similar needs and can
provide valuable insight into what worked and what didn’t. Given the
costs of a large storage system, you can’t afford to do it wrong.
After you have an idea of
what you want to implement, find out if you can contact references to
determine if they were happy with the solution they implemented. Some
companies try to get you to commit to the latest and greatest versions
of their software and firmware. Large storage environments are a big
investment and business processes depend heavily on it. Ensure that you
are implementing a stable and well-tested solution.
Tip
A tremendous number
of options are available when it comes to storage solutions. When in
doubt about a decision, always refer to the original goals of the
project and ask yourself, “Does this decision support the goals of the
project?”
Developing the Storage Solution
After you have
determined the needs, explored the options, and come up with a plan, the
real fun can begin. Any solution that will become part of the critical
path of business must be developed and tested in a controlled lab
environment. This is the part of the project where policies and
procedures start to take form. Practice runs of mirroring, failing over
of resources, and recovery of systems ensure that the solution will be
able to support the needs of the company.
During this development
phase, practice connecting your servers to the SAN or NAS. Develop and
document standards around HBAs or network interface cards (NICs), the
versions of firmware that will be used, and the version of the drivers
that will be used. Most SAN and NAS manufacturers provide a detailed
list of supported combinations of hardware, firmware, and software.
Deviate from these approved lists at your own risk. The last
thing you want to implement is an unstable storage environment because
you chose not to follow the recommended configurations.
The development
phase will identify several requirements that are not usually thought of
during the planning phase. Most specifically, these requirements are in
the area of facilities. Most SAN devices are fairly large. An EMC
Symetrix and Connectix, for example, will take up a full rack each. With
heat generation more than 3,000BTUs, HVAC resources will need to be
considered. Also keep in mind that most SAN and NAS solutions require
220V to run them. Ensure that planned data center locations have
appropriate space, cooling, and power. Power should include not only the
standard AC feed, but battery backup as well. Be aware of any special
requirements of the SAN or NAS. Some SAN devices on the market void
their warranty if they are placed within 5 feet of any solid objects.
Tip
Be sure to carefully
document the entire installation and configuration process. It not only
makes troubleshooting easier, but it also provides the full road map
for pilot implementation.
