The world of storage can be
forbidding to a novice. Even veteran IT personnel may be put off by
the sheer volume of new terminology and alphabet soup that has
evolved. Before we dive in, let's sample some basic terms. This is
by no means a complete list of key definitions, but it should make
things clearer, or at least be enough to make this article
Direct Attached Storage (DAS)
The server stores data on disks that are in the same box. Redundant
Array of Independent Disks (RAID) is used heavily in this approach.
A collection of computers and devices are connected over a
high-speed network and are dedicated to the task of storing and
protecting data. Instead of storing data locally, each server sends
data across the network to a shared pool of storage.
A large array of disks in one box, it is often used as part of a SAN
to store data for multiple servers. These servers typically connect
to the disk array using Fibre Channel.
Optical fiber cables transmit data at high speed in a SAN. Fibre
Channel is the transport protocol used for this purpose.
Network-Attached Storage (NAS)
NAS separates data from applications by storing data on filers
attached to the LAN. Filers can share files across multiple
applications, platforms, and operating systems.
Computer Systems Interface (iSCSI)
This standard enables storage and retrieval at high speed (1
GB/second or higher) over regular IP networks.
More Key Terms To
Direct Attached Storage (DAS)
Area Network (SAN)
Fibre Channel (FC)
Network-Attached Storage (NAS)
Small Computer Systems Interface (iSCSI)
Refers to various techniques and devices for storing large amounts
The hardware that connects workstations and servers to storage
devices in a SAN is referred to as a "fabric."
Short for Redundant Array of Independent (or Inexpensive) Disks, a
category of disk drives that employ two or more drives in
combination for fault tolerance and performance.
Storage virtualization is the amalgamation of multiple network
storage devices into what appears to be a single storage unit.
Storage virtualization is often used in SAN (storage area network).
Basic Strategy Keep it Simple
Storage is an immense and complex universe. Once you enter, your mind is
soon swimming in strange, even alien concepts. Therefore, it is best to
stick to what you know and keep it very simple especially at the start.
One obvious way to avoid complexity is to use the services of a storage
service provider. These are firms that lease storage from their own data
centers and other services. The advantage of a storage provider is that the
vendor provides a variety of storage options for a fixed cost. This is a
handy way to add storage capacity or meet regulatory compliance/archiving
requirements without having to build new infrastructure.
Of course, simplicity can be taken to
extremes (i.e., attempting to pass the entire storage burden to an external
source or keeping everything stored on the same old servers using bigger and
better disks). Such a strategy eventually runs into a wall; there is so much
data stored on so many servers that it becomes impossible to manage.
Beyond DAS, then, where should the rookie
storage guy go to ease his woes? Initially, at least, it might be smart to
start with NAS and avoid SANs. At its core, a NAS filer is simply a
specialized type of server that connects to the network. Storage is rapidly
added by plugging the appliance into a network hub or switch. The likelihood
is that the server administrator will run into very little that is new to
him by buying a NAS box.
The drawback of NAS is that filers and
servers share the same LAN. As a result, network performance may eventually
be affected. When that juncture is reached, it may be remedied by upgrading
the LAN and adding higher-grade NAS equipment. A more long-term solution
would be to roll out the first SAN.
Undoubtedly, the land of the SAN can be forbidding. Continuing with our
theme of simplicity, the transition to a SAN can be made smoother by
beginning with rapidly maturing iSCSI technology. iSCSI allows the
establishment of a SAN over an IP network. Thus, the IT department does not
need to learn new protocols or add new skill sets to create a SAN. This also
has the advantage of being much less-expensive than an FC SAN.
iSCSI is especially appropriate for companies
with IP backbones capable of handling gigabit traffic. While the technology
is improving rapidly, it doesn't offer the same speed or capacities as a
heavy-duty FC SAN. Similarly, SANs offer higher speeds and throughput than
NAS systems. To do this, they offload data traffic to a separate network for
On the negative side of the ledger, however,
SANs may have difficulty supporting multiple operating systems and
platforms. In addition, some users complain about being unable to integrate
SAN solutions from different vendors. SANs don't have to be that big to be
valuable or affordable, but they are made up of highly specialized
components that require strong internal expertise.
The basic strategy for storage is to try to stick with the familiar. NAS
and iSCSI are good starting points for competent IT departments already
familiar with IP networking. FC SANs, on the other hand, should probably be
avoided unless you have very large capacity and require the highest possible
performance. If so, it is best to recruit a dedicated storage team to
wrestle this beast and bend it to your corporate will. Although the cost and
complexity are greater in the short term, the potential long-range payoff is
greater than with NAS or iSCSI.
And for those that just don't want to involve
themselves in yet another IT skill set, managed storage services now cover
the entire spectrum. Sometimes it is just less-expensive, easier, or faster
to call in the professionals and leave everything to them.
Did You Know...
The basic strategy for storage is to try to stick with the
familiar. NAS and iSCSI are good starting points for competent
IT departments already familiar with IP networking. FC SANs, on
the other hand, should probably be avoided unless you have very
large capacity and require the highest possible performance.
~ By Drew Robb
This article was adapted from Server Watch.
The full article can be found
Last updated: February 03, 2006
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