Tight rope walk



Usually, it is traumatic for a CIO to decide over a SAN implementation.
Having done that, and having obtained the funding for one, it is even more
traumatic to choose between an IP SAN or FC SAN. Both are luring. While the cost
of one is lucrative, the appeal of the other’s high speed is enough to entice
an unsuspecting buyer.

Choice A Plenty
The decision to go for one or both or a combination of the two must be based
on the same factors that led the organization to decide to go for a SAN.

Vivekanand Venugopal, director, Software Solutions, APAC, Hitachi Data
Systems, says, “The intelligent buyer would use the application to dictate the
technology selection.” Customers can match the right applications to the right
technology, if they have clearly differentiated their key applications based on
performance, availability, cost, and manageability.

If the decision to adopt either FC or IP based SAN technologies is taken
logically, the organization will find itself going for a combination of the two.
The reason is simple. Rahul Gupta, vice-chairman, SNIA (he is also managing
director of Xserves) says, “If you talk of 20 TB storage on fiber channel, it
will cost you the moon.” So in architecture, the critical data can be put on
fiber channel, with FC drives; while the rest of the data can be in IP SAN with
SATA drives.

Fiber channel architecture is preferred when there is requirement in a local
environment for a very high-speed data transfer between the main network and the
storage network. But over a WAN or in a multi-location environment, where data
needs to be replicated, then probably an IP SAN could be a better option. This
is because TCP/IP is simpler protocol that is understood by almost all the
system administrators. Implementing fiber channel is a little more complex
besides being more expensive.

Anand adds, “When we do applications profiling for customers, we try and
understand what applications would be categorized. Say, as class A, which is
high performance, high availability, high recoverability, and very high response
times. Also, for these applications we will recommend a fibre channel-based
network. Because it is the most deterministic network available because of its
maturity.”

The Work Profile
Besides cost, speed is the primary difference between the two, and all other
differences flow from that.

IP vs FC

Besides speed and
costs, there are a few other differences between the FC and IP variants of
SANs. However, it must be kept in mind that these come into play, only if
other factors remain the same.

  • Familiar network
    technology and management: This implies not only an ease of rollout
    but also reduces training and/or hiring new staff for new
    technologies.

  • IP is a proven
    transport infrastructure.

  • IP SAN can easily
    help an organization transition from requirements of 1 Gigabit
    Ethernet to 10 Gigabit Ethernet. Unless the organization’s needs are
    beyond that, IP SAN can help it protect the investment and upgrade the
    performance of its infrastructure in a very simple manner.

  • Over long distance,
    there is no need for investing in fiber channel extenders. Thus, it
    simplifies remote data replication and disaster recovery.

  • Because IP SAN can
    leverage on existing Ethernet resources and skill, it leads to lower
    total cost of ownership.

The fiber channel standard achieves its high performance by assigning much of
the protocol processing to the dedicated hardware, a fiber channel host bus
adapter or a fiber channel switch. For applications of real-time data transfers,
such as e-commerce or online transactions, fiber channel is preferred.

While laying a fiber over a long distance may not be very feasible, the fiber
channel protocols can still be employed over WANs, by bridging the storage
solutions with dedicated bandwidth over leased lines or satellite connectivity.
It is important that the data carrying capacity of the media (fiber or
otherwise) be matched with the capacity of the HBAs and the FC switches.
Otherwise, the investment in them will be wasted.

IP SAN solutions are more useful where customers are looking for low-cost
solutions to block I/O applications, rather than file sharing applications. Some
of these block I/O applications could be deployment of exchange, SQL servers,
Linux-based database and backups. These are typically mission important, not
necessarily mission critical applications. They can function satisfactorily with
lower I/O and availability requirements.

Data and Traffic Analysis
Over the choice of use of FC SAN or an IP SAN, besides the needs of the
applications and the volume of data generated, the traffic analysis is also an
important factor. Thus, even if a branch office is generating huge amounts of
data, there may not be enough justification in putting up a fiber channel
solution there if the users of that data are sitting in the head office.
Whereas, if all this data is consolidated at one place and then viewed by a
large number of users, the FC SAN seems to appear viable.

What To Do For DR?
Today majority of the DR solutions have used IP circuit as a replication
mechanism. The cost of an FC circuit is as big a factor as the FC hardware, in
deciding to go for an FC solution. However, there is always a lag between the
primary and the secondary site. One solution to that is deploying a pre-datacenter
solution. According to Anand, many customers today say, “I would like to have
near zero loss and implement long distance replication as well.” The pre-data
center solution has a primary site and a secondary, which would be synchronous
over fiber channel over short distances. From the secondary site to the tertiary
site (which can be across states) will be over an IP circuit and an asynchronous
replication. With this kind of replication, near zero data loss implementations
can be achieved.

Some of the organizations that have implemented this type of pre-data center
solutions are HDFC Bank and Infosys.

Gupta says, “As far as loss is concerned, all vendors provide software to
ensure that the data packets that go from one place to another have been
acknowledged. So there is no question that data could get lost in transit.” In
DR kind of situations, if there is a file sharing kind of situation, and the
data has to be replicated in real time, an FC SAN over a dedicated leased line
bandwidth would be preferred. But if the replication can be done over a period
of time, then IP SAN will be fine. Another important issue is that from the same
database, or from the same storage network, how many people would simultaneously
access one type of data. If the number increases, the argument will shift
towards fiber channel.

Can a Fat IP Pipe compensate for an FC Solution?
No. Although it may imply that, it is not exactly like that. The difference
is that even if you have a huge pipe, the hardware on both sides of that pipe is
equally important. When talking about a video kind of application, a few frames
getting skipped won’t matter. But if it is a critical online transaction, you
cannot afford jitter or loss of data. Since fiber channel is the more
deterministic of the two, for the second type of applications, it scores over
pure IP deployments. Though solutions like FCIP and IFCP run over IP media,
their protocols are different therefore their manageability would also be
different.

One major advantage of an IP SAN is that it can leverage the organization’s
existing investment in the IP circuits and hardware, whereas, fiber channel will
require new and heavy investments. For this reason, SMEs are also driving the
demand for IP SANs, which have been picking up in the last one year.

Virtualization too does not seem to be taking sides between the two, allowing
the two to coexist. In an storage architecture, one can also have half portion
running on FC SAN and another half on IP SAN.

While in an environment an FC SAN can work over copper, it restricts the
capabilities of the fiber channel hardware. The SAN is a solution. Its fastest
speed is that of the weakest or the slowest link. So, the cost savings by
putting in copper have to be compared with the investment in expensive HBAs, FC
switches, and high- speed storage media and servers. Also, it requires
additional investments in the form of fiber channel extenders to be made. The
investment in fiber channel extenders is a big factor to keep while choosing to
route FC over IP.

On the whole, FC adoption is not determined only by the cost of circuits, it
is also determined by response times, round-trip response ties etc, which IP
cannot match, it is not that deterministic. That is where fiber channel
outscores.

At the same time, using fiber channel over IP is a more reliable
architecture, says Venugopal, because of its higher performance, compared to a
pure IP SAN.

By translating fiber channel control codes and data into IP packets, fiber
channel functions over IP. It is sometimes also called fiber channel tunneling
or storage tunneling.

A lot of the issues in the FC versus IP debate could be resolved in the
coming days with two simultaneous happenings. One, the cost of fiber channel
circuits is reducing, at the same time storage virtualization will allow system
administrators to manage the two seamlessly from one console. The two will form
part of one solution, without causing any pain to the administrators.

The Damages
Obviously in terms of absolute cost, IP SAN is less expensive than FC SAN.
Whether one takes HBA, or any other element that goes into the SAN, in case of
fiber channel it is extremely expensive as compared to whatever he uses in the
IP SAN.

Is There a Better Technology?
The test and R&D houses have been churning out reams of data on how FC
SAN has actually ‘proven’ to be less ‘efficient’ compared to iSCSI. But
that knowledge does not seem to have gone down to the market, with FC SANs still
remaining popular. One reason could be that a SAN is primarily an
enterprise-class solution. For lesser organization, a NAS may serve the
purposes. Of course, with growing business needs, even SMEs 
need consolidated storage that can be easily managed. But, the
deterministic nature of fiber channel, and the reliability it has shown over the
years are still a big factor why the enterprises are going for it.

There is also an allegation that the popularity of FC SANs is vendor driven.
It is alleged  that the technology
is expensive. More importantly, many of the vendors are currently not ready with
a competitive IP SAN solution; they are pushing FC SANs to the customers. The
customers, forced with an artificially created lack of choice, have no option
but to go for what is made available by most of the vendors.

However, most vendors vehemently deny the charge. Venugopal says, “We
don’t lead with the technology platform. Typically, we recommend a strategic
application optimized storage.” What this means is that customers view their
applications first and then optimize the storage infrastructure to meet the
storage requirements.

There are advantages that SAN can offer, advantages that may not have been
part of the original scheme of things in deciding to go for a SAN. Harish Shetty
of HDFC Bank says, “When we moved the applications from a DAS environment to a
SAN environment, we had to revisit the way we used to do our backups.

The process change actually allowed us to free the production servers for the
end of day activities.” This could happen because the backups now happen using
the off host server. While the bank’s primary purpose of going in for a SAN
was for the purpose of protecting data by replicating the same to a DR site.
This also allowed the bank to reduce the amount of time for which the system was
taken down for the purpose of end of day activities. The bank, as Venugopal
pointed out, has a pre-data center solution, whereby it capitalizes on the
abilities of the SAN technologies, fiber channel as well as IP.

Alok Singh
aloks@cybermedia.co.in

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