Exabyte Corporation
1685 38th Street
Boulder, CO 80301
1-800-EXABYTE
www.exabyte.com
An Exabyte White Paper
Why Choose Native Fibre
Channel Backup?
Optimal protection for the SAN
Lynda Edgington
Exabyte Technical Publications
Executive summary
For years, SCSI-based tape drives and tape libraries have provided
effective backup for traditional business networks. These networks
employ server-attached storage—disks attached to the network through
servers that control the data. Backing up server-attached storage
typically involves sending data across the network to tape libraries
attached to backup servers. These massive data transfers degrade
network performance and prevent servers from concentrating their
resources on other business processes.
Traditional server-attached storage is rapidly giving way to storage area
networks (SANs). Businesses are adopting Fibre Channel SANs to
alleviate the data storage and delivery problems associated with
ever-increasing data loads. SANs provide data availability, shareability,
and manageability that is not possible with server-attached storage.
Businesses making the switch to SANs are finding that they have a
tremendous opportunity to upgrade their backup operations. By
attaching Fibre Channel tape drives and libraries directly to the SAN, a
business can back up its network more quickly, eliminate network
slowdowns during backups, make more efficient use of backup
resources, and simplify backup and recovery administration.
Exabyte provides leading-edge native Fibre Channel tape drives and
libraries that attach directly to the SAN without the use of intervening
routers. Exabyte libraries, featuring Mammoth-2 (M2) tape drives,
support serverless backup in which data can be moved directly from
disk to tape without the involvement of a server. With Exabyte’s native
Fibre Channel backup devices, your backups can finally be completely
transparent to users and processes on your network.
July 2001
CS0599.00
Why Choose Native Fibre Channel Backup?
July 2001
Where we are today
Businesses are scrambling
for computing solutions that
can manage extreme data
loads with unprecedented
speed and accuracy.
When asked to name the most important factor affecting today’s business
computing decisions, IS professionals have an immediate reply:
explosive data growth. Businesses are scrambling for computing
solutions that can manage extreme data loads with unprecedented speed
and accuracy. With our increasing reliance on such applications as
internet commerce, enterprise resource planning, and on-line transaction
processing, the requirements are clear: Data must be available
cross-platform, cross-application, without delay, and without error.
To meet these requirements, Fibre Channel storage area networks
(SANs) have emerged as the top solution for delivering data. Fibre
Channel is a standard for information delivery that enables large data
transfers at very high speeds with minimal network protocol overhead. A
SAN is a Fibre Channel network that is separate from a business’s
regular network. The SAN is dedicated to storing, backing up, and
delivering data to and from users, servers, and storage devices. SANs
speed up data delivery, allow more efficient use of storage resources, and
simplify data management.
You may be in the process of implementing a SAN for your business, or
you may be evaluating such a move. We will discuss the many benefits
of SANs later in this paper. For now, we will focus on a specific aspect of
network management: the dreaded data backups. As you will see, if you
are in the process of moving to a SAN to alleviate your storage problems,
you can reap the added benefit of no-hassle backups by employing Fibre
Channel backup devices on your SAN.
The backup picture
There is no question that backups are essential for data-intensive
businesses. Operating without a backup strategy means risking
everything. Tape backup is a proven technology that is cost-effective and
reliable. That’s why most businesses employ tape drives or tape libraries
to back up critical data.
If your business network is like most, you probably have a
well-established Ethernet-based system connecting your users with
application servers, file servers, and each other. Your network includes
various servers dedicated to specific business processes, like resource
planning, transaction processing, accounting, e-mail, and such. These
servers typically have their own dedicated server-attached storage—
disks attached directly to the server.
Page 2 of 12
July 2001
Why Choose Native Fibre Channel Backup?
Initially, you may have met your backup needs by connecting a
SCSI-based tape drive or small tape library to each server to back up that
server’s disks. This is traditional server-attached backup. As the amount
of data and number of servers increased, you probably consolidated your
backups by attaching a larger library to a dedicated backup server and
sending data across the network to be backed up.
Do backups give you nightmares?
As critical as backups are to business, they are arguably the least-loved
aspect of network administration. Backups are notorious for bogging
down networks.
As data volumes increase,
network delays during
backups are reaching
unacceptable levels.
Most network protocols in use today were designed for infrequent
transfers of small files and the exchange of instructions between users
and processors. When handling large amounts of data, these protocols
introduce significant overhead. During backups, networks suffer not only
from traffic volume, but from data transfer inefficiencies. As data volumes
increase, network delays reach unacceptable levels.
In addition to causing network slowdowns, backups also monopolize
servers. During backups, servers must devote a high percentage of their
processing power to pulling data from network disks and sending it to
tape drives. These servers are prevented from devoting their full
resources to other important business applications.
To avoid these problems, you try to schedule your backups for off-hours
or weekends. However, if you are a 24x7 business, there may be no
appropriate down-time for backups. You may be forced to accept routine
sluggish network performance, or you may be backing up less often than
you would like to avoid slowing down business.
As if squeezing backups into an ever-shrinking backup window isn’t hard
enough, you have to deal with managing all of the backup systems
scattered throughout your network. You have to visit multiple locations
and use a variety of software packages to set backup schedules. You
have to verify that backups complete and you must collect tapes. You
have to perform routine maintenance and troubleshoot problems. And,
with constantly increasing data volumes, you frequently have to install
new backup devices and reconfigure servers to support them.
The ultimate aggravation is that you are devoting significant resources to
keeping your backups running—resources that are doing nothing to
enhance the performance of your network.
Page 3 of 12
Why Choose Native Fibre Channel Backup?
July 2001
Why do we do this?
We continue to put up with backup nightmares because server-attached
backup has been the only effective option for years. SCSI-based backup
devices have served us well in server-attached configurations because
SCSI is ideal for transferring data between two devices over short
distances. SCSI supports large data transfers and offers extremely fast
transfer rates (currently up to 160 MB/second). These capabilities are
exactly what is needed for server-attached backup.
However, businesses are finding that data has reached a critical mass
that threatens to bring down the network unless a new approach is found.
As server-attached storage gives way to SANs, backup strategies must
also evolve to keep pace with the benefits provided by the SAN.
Businesses are turning to SANs
SANs offer businesses a way
to solve their data storage,
management, delivery, and
backup problems.
Over the past few years, SANs have evolved from a concept promising
great benefits to a rapidly-maturing technology embraced by many
businesses. SANs offer businesses a way to solve their data storage,
management, delivery, and backup problems.
Some of the dramatic benefits of SANs are:
Quicker data delivery. Data transfers take place on the Fibre
Channel SAN rather than the production network. Fibre Channel
currently transfers data at 100 MB/ second. In the near future, speeds
of 200 and 400 MB/second will be common. In comparison, widely
used 100BaseT Ethernet transfers data at approximately 10 MB/
second.
Better network performance. Network slowdowns are eliminated
because the SAN frees the production network from the task of
transferring huge amounts of data.
More efficient use of storage. Storage is not tied to specific servers,
so it becomes a pooled resource. Storage can be allocated as
needed, resulting in less under-use or over-use of individual storage
devices.
Increased data accessibility. Data can be shared among all servers
attached to the SAN. Fibre Channel allows multiple devices to access
the same data, regardless of platform, physical interface, operating
system, or data protocol.
Easier scalability of storage. An administrator can hot-plug
additional storage into the SAN as needed, without having to bring
down the network or reconfigure servers.
Page 4 of 12
July 2001
Why Choose Native Fibre Channel Backup?
Improved fault tolerance. Multiple data pathways, mirroring
capability, and reduced error rates provide a highly reliable data
transfer system. If a server or data path fails, alternate routes through
the SAN are available.
Improved storage manageability. An administrator can monitor and
control all of the SAN’s storage from a single remote console.
How does a SAN improve backups?
While SANs are deployed primarily to remedy data storage problems,
tremendous benefits also come in the area of data backups. These
benefits parallel those just mentioned.
Quicker backups
With tape libraries attached directly to the SAN, data to be backed up is
sent through the SAN rather than the production network. Backups take
place more quickly because the Fibre Channel SAN moves data much
more quickly than the typical Ethernet-based network. If the SAN
supports serverless backup (described on page 9), backups can take
place even more quickly because server bottlenecks are eliminated.
Better network performance
With data moving across the SAN rather than the production network, the
network no longer bogs down during backups. Backups can take place at
any time without impacting network users.
More efficient use of backup resources
Backup resources are used more efficiently because capacity can be
shared among all the devices on the SAN. Because storage is no longer
tied to specific servers, data can be directed to any backup device on the
SAN that has the appropriate capacity.
Greater accessibility to data for recovery
Because storage devices aren’t tied to particular servers, data recovery
doesn’t have to be tied to a particular server’s backup device. Just as
backups can be sent to any tape drive on the SAN, recovery can take
place from any tape drive. The data is simply directed through the SAN to
the affected storage device. Tapes can be managed at a central location,
and recovery can be controlled from a single console.
Page 5 of 12
Why Choose Native Fibre Channel Backup?
July 2001
Easy scalability
When additional backup resources are required, an administrator can
hot-plug devices into the SAN without reconfiguring servers. Unlike the
limited number of devices supported on a SCSI bus, the SAN can support
enough backup capacity to meet the needs of the entire network. The
most common Fibre Channel networks implemented today can support
over a hundred devices. The Fibre Channel standard defines other
configurations that can support thousands to millions of devices.
Improved fault tolerance
Backup operations are more fault tolerant on a SAN because Fibre
Channel provides multiple pathways for data. If a data path fails, data
can be routed through a different data path. Likewise, if a tape drive fails,
data can be backed up to another tape drive on the SAN. For additional
fault tolerance, data can be copied to multiple devices on the SAN,
including devices at remote sites. Depending on the type of cabling used,
data can be transferred up to 10 kilometers (6.2 miles) between Fibre
Channel devices, allowing direct remote data duplication.
Simplified backup management
The management of backups is much easier because backup devices
can be centrally located and monitored from a single console. Because
backup resources are used more efficiently, there are fewer devices to
monitor and maintain. Because resources are pooled, they can be easily
allocated as needed through software.
Fibre Channel backup from Exabyte
Exabyte has always understood the importance of providing
cost-effective, reliable backup solutions. With the emergence of SANs,
these solutions must also integrate seamlessly into the Fibre Channel
network.
With SAN applications in mind, Exabyte has introduced three native Fibre
Channel libraries. The 430M, X80, and X200 MammothTape libraries,
shown in Figure 1, feature Exabyte’s award-winning native Fibre Channel
M2 tape drives. Each library and its tape drives connect directly to the
Fibre Channel SAN without the need for intervening routers.
True native Fibre Channel
connectivity and serverless
backup support make the
Exabyte 430M, X80, and
X200 ideal for backing up
the SAN.
Page 6 of 12
The M2 tape drive is the first midrange tape drive with native Fibre
Channel connectivity, as well as the first in its class to provide built-in
serverless backup support. Serverless backup, described on page 9,
allows backups to proceed directly from disk to tape without server
involvement. True native Fibre Channel connectivity and serverless
backup support make the 430M, X80, and X200 ideal for backing up the
SAN.
July 2001
Why Choose Native Fibre Channel Backup?
The Exabyte 430M Library
• 4.5 TB capacity (compressed)
• 432 GB/hour transfer rate (compressed)
• Up to four M2 tape drives
• Up to 30 tapes
• Standalone or rack-mountable
• Supports serverless backup
The Exabyte X80 Library
• 12 TB capacity (compressed)
• 864 GB/hour transfer rate (compressed)
• Up to eight M2 tape drives
• Up to 80 tapes
• Standalone or rack-mountable
• Supports serverless backup
The Exabyte X200 Library
• 30 TB capacity (compressed)
• 1 TB/hour transfer rate (compressed)
• Up to ten M2 tape drives
• Up to 200 tapes
• Standalone or rack-mountable
• Supports serverless backup
Figure 1
Exabyte’s SAN-ready native Fibre Channel libraries
Page 7 of 12
Why Choose Native Fibre Channel Backup?
July 2001
Native vs. non-native Fibre Channel
The importance of native Fibre Channel for effective SAN backup cannot
be overemphasized. The benefits discussed in this paper rely on backup
devices being connected directly to the SAN.
When Fibre Channel SANs first came into being, an effort was made to
enable tape drive and library owners to connect their SCSI-based backup
devices to the SAN. This led to the development of SCSI-to-Fibre
Channel routers that translate device mapping and addressing protocols
between the two interfaces.
SCSI-to-Fibre Channel
routers are less than ideal
for effective backup in
mature SAN environments.
SCSI-to-Fibre Channel routers were useful in early SAN implementations
because they allowed users to experience many of the benefits of SANs
without having to scrap expensive backup equipment. However, these
routers have a number of drawbacks that make them less than ideal for
effective backup in mature SAN environments:
Routers cause performance bottlenecks. When multiple tape
drives in a library are connected to the SAN through a router, all of the
data to and from the drives passes through just one or a few Fibre
Channel connections. Forcing what should be multiple data streams
into a fewer than optimum number of channels makes it difficult to use
the full streaming capability of each tape drive.
Routers introduce potential failure points. When a library and its
tape drives are connected to the SAN through a router, failure of the
router takes the entire library and its drives out of service, even when
they are functioning perfectly.
Routers are difficult to configure. An administrator must work with
complex address mappings to assign multiple SCSI IDs to a single
Fibre Channel connection. In addition, the router must be
reconfigured each time a new device is added.
Routers aren’t scalable. A lIbrary’s capacity can be expanded by
adding tape drives, but if the router’s total bandwidth is already in use,
the router must be replaced to accommodate the additional drives.
Routers are expensive. Routers can cost well over $10,000.
As SAN administrators routinely upgrade their backup systems, they are
turning to native Fibre Channel systems that eliminate the need for routers.
Without the router, library and tape drive performance is used more
effectively because data no longer has to pass through a fewer than
optimum number of Fibre Channel connections. When connected
through a hub, multiple drives in a Fibre Channel library can be kept
streaming (up to the hub’s data rate limit). When connected through a
switch, all of the drives in a library can easily be kept streaming.
With a library connected directly to the SAN, the potential failure point at
the router is eliminated. Failure of this single piece of equipment can no
longer take out the entire library.
Page 8 of 12
July 2001
Why Choose Native Fibre Channel Backup?
Library capacity and performance can be expanded by simply adding new
drives, without the configuration hassles of a router. Drives can be
hot-plugged into the library without interrupting library or SAN operations.
Note that while some tape libraries claim to be native Fibre Channel, they
really just contain an integrated router. If the internal router fails, the
entire library and its drives are out of commission. The router cannot
simply be swapped out, so repair is expensive and time-consuming.
True native Fibre Channel libraries from Exabyte eliminate the router
failure point and provide enhanced reliability, throughput, and
cost-effectiveness for the SAN.
Serverless backup removes the server bottleneck
Even though backups are
quicker on the SAN, data
does not flow optimally
between storage and backup
devices because servers are
involved.
Without question, sending backups through a SAN relieves networks of
the problems associated with massive data transfers. However, even on
a SAN, most backup systems require servers to process the data
transfers. The server itself becomes a bottleneck as data moves from
disks on the SAN to server memory, then from server memory to tape
drives on the SAN. Even though backups are quicker on the SAN, data
still does not flow optimally between storage and backup devices because
servers are involved.
In addition to the performance bottleneck, managing data transfers during
backups prevents servers from using their full resources on other
important tasks, such as running applications and processing data. As a
result, although the backup window is not as tight as it was before the
SAN, it still exists. Backups must still be scheduled when they have the
least impact on users and business processes running on the servers.
Exabyte’s M2 tape drive eliminates these performance impediments by
providing built-in serverless backup, a process by which data goes
directly from disk to tape on the SAN, without traveling through a server.
Serverless backup is sometimes called “extended copy” or “E-copy”
because it is based on the SCSI Extended Copy command. As shown in
Figure 2, a server simply issues an Extended Copy command to the tape
drive through its application software. The command specifies the data’s
location and how much is to be transferred. The tape drive then assumes
control of the actual data movement between disk and tape.
With serverless backup, network administrators see significant
cost-saving benefits above and beyond those already achieved through
the SAN:
Backups occur more quickly since server bottlenecks no longer exist.
Dedicated backup servers can be eliminated.
Application and file servers that double as backup servers can be
made fully available for other business-critical tasks.
Page 9 of 12
Why Choose Native Fibre Channel Backup?
Bypassing the server boosts
backup performance,
eliminates backup window
constraints, and allows
servers and backup devices
to be used more efficiently.
July 2001
Tape drive speed is better utilized because data can be streamed
directly to tape instead of being held up by server performance
limitations.
Backups can take place at any time without impacting the network or
servers, completely eliminating the concept of a limited backup
window.
Data recovery is quicker because frequent “snapshots” of the network
are more convenient to perform; backup tapes contain more recent
versions of data, so there is less work to recreate and business can
resume more quickly.
Local Area Network
Server
1 Server issues Extended Copy
command across SAN to tape drive
2
Disks
Fibre Channel switch
Tape drive
4
3
Figure 2
Tape drive instructs
disks to read and
send data
Tape drive writes
data to tape
Disks send requested data
across SAN to tape drive
Serverless backup between disks and a tape drive on a Fibre Channel SAN
Be aware that some tape systems implement serverless backup by
attaching a storage router that manages the data movement between the
SAN and the tape drive. Exabyte’s M2 is the first tape drive to offer
built-in serverless backup support. The router—an expensive piece of
equipment that is a potential point of failure and a source of performance
bottlenecks—is unnecessary.
Page 10 of 12
July 2001
Why Choose Native Fibre Channel Backup?
What if you aren’t ready for a SAN?
If you’re not quite ready to implement a SAN, should you stick with SCSI
or move to Fibre Channel when you need to add more backup resources?
Even if you don’t have a
SAN, SCSI limitations may
make Fibre Channel a
better choice for your
backup systems.
While SCSI is a well-established, reliable standard for backup devices,
you may find that SCSI backup is no longer sufficient for your expanding
network. SCSI limitations on distance between devices, number of
devices supported, and bandwidth shareability may make Fibre Channel
a better choice for your backup systems.
Distance between devices
SCSI is capable of high data transfer rates (up to 80 MB/second for Ultra2
SCSI and 160 MB/second for Ultra3), but these rates can only be
achieved over short distances (up to 12 meters for multiple devices).
Fibre Channel can support distances of up to 10 kilometers between
devices while still providing high data transfer rates (100 MB/second now,
200 and 400 MB/second in the near future). The distance capabilities of
Fibre Channel not only facilitate remote backup, but open up options for
the placement of backup devices within a business facility.
Number of devices
The maximum number of devices that can be connected to a wide SCSI
bus is 16. This inhibits sharing of tape libraries between servers because
a large library and its drives may use up most of the available SCSI IDs.
The basic Fibre Channel configuration, an arbitrated loop, can support up
to 126 devices, and switched fabrics can support millions of devices.
Even without a SAN, you can easily share a Fibre Channel tape library
among multiple servers and their disk systems.
Bandwidth shareability
All of the devices on a SCSI bus must share the bandwidth of the bus.
This means that all of the tape drives in a library may be competing for
bus access at the same time. When multiple devices are attached to a
SCSI bus, complex arbitration and addressing protocols are required to
control bus access and manage data flow. The processor overhead
required to manage the bus degrades the performance of all the devices
on the bus.
In contrast, Fibre Channel provides greater bandwidth with simpler
arbitration and addressing protocols. In a Fibre Channel arbitrated loop,
tape drives take turns as on a SCSI bus, but access to the bandwidth is
more efficient. In a switched fabric, all of the tape drives in a library can
use the full bandwidth of Fibre Channel simultaneously.
Page 11 of 12
Conclusion
July 2001
Look to Fibre Channel for backup
If the volume of data on your network is expanding rapidly, as it is on
nearly all networks, consider phasing in Fibre Channel backup devices
even if you aren’t ready for a SAN. Many servers that control large disk
systems either already have Fibre Channel interfaces or are upgradeable
to Fibre Channel through the addition of host bus adapters. You can
connect a standalone Fibre Channel M2 tape drive directly to the server,
or you can connect a Fibre Channel library through a hub or switch.
Whether or not you are contemplating a SAN, Fibre Channel backup
devices will serve you well in your present situation and can be easily
integrated into a future SAN if you choose to go that route.
Conclusion
Fibre Channel SANs are rapidly emerging as the architecture of choice to
meet the data delivery requirements of today’s businesses. SANs greatly
improve data availability, shareability, and manageability over traditional
networks that use server-attached storage. Businesses that implement a
SAN save a significant amount of money through more efficient use of
storage resources, greater productivity, and reduced administrative costs.
As on any network, backup on the SAN is essential. While backups on a
traditional network can cause considerable headaches, backups on the
SAN are pain-free. With a SAN,

Backups take place more quickly
The impact of backups on network performance is eliminated
Tape drives and libraries are used more efficiently
Data is more accessible for recovery
Backup capacity can be added easily
Fault tolerance during backups is increased
Backups are easier to manage
The key to effective SAN backup is attaching tape drives and tape
libraries directly to the SAN. While SCSI tape drives and libraries can be
attached to the SAN through routers, backup devices need native Fibre
Channel interfaces to avoid creating data bottlenecks and bringing
unnecessary complexity and cost to the SAN.
© Copyright 2001 by Exabyte Corporation.
All rights reserved. Exabyte, Exabyte
Recognition System, Exafacts, Exapak,
Exasoft, Exatape, and Strategex are U.S.
registered trademarks of Exabyte
Corporation. Eliant, M2, MammothTape,
NetStorM, SmartClean, and SupportSuite
are U.S. trademarks of Exabyte
Corporation. All other product names are
trademarks or registered trademarks of
their respective owners.
Page 12 of 12
Exabyte is the first company to integrate a native Fibre Channel interface
into its tape storage devices. The 430M, X80, and X200 libraries with M2
tape drives attach directly to the SAN without intervening routers. These
libraries are also the first to support serverless backup, which eliminates
server bottlenecks, allows server resources to be applied to other
processes, and makes the concept of a limited backup window obsolete.
Exabyte designs its libraries with the reliability, scalability, and
manageability required for storage area networking. With native Fibre
Channel and serverless backup support, the 430M, X80, and X200
libraries provide optimal protection for the valuable data on your SAN.