by Patty Barkley,
Storage Networking Market Manager,
CNT - (February
2003)
storage news
Disk to disk backup
Virtual Tape: Can You
Afford to Ignore It?
Compared to
EMC... our all flash arrays are better
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| Editor's intro:- CNT
has often
appeared
in news stories we've run about wide area
internet storage. I
asked CNT to tell our readers some of the things they can in real life
applications with this new technology. This article is the result. | |
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| Using
Remote Disk and Tape for Business Continuity/Disaster Recovery |
Overview
Businesses today are increasingly aware that the dangers to their
mission-critical data are greater than ever before. Government agencies and
private disaster planners are urging businesses to establish BC/DR systems that
separate primary and backup sites by at least 200 miles, instead of the typical
60 miles. The SEC and Federal Reserve are calling for businesses that play a
significant role in financial markets to establish fully redundant backup sites
at least 300 miles offsite and be able to recover critical activities on the
same business day of a disaster.
Tape has long been an affordable backup medium. However, when it came
to remote data replication, tape had severe limitations. With heavy latency
impact over as little as a 10-mile distances, remote tape backup was not a
viable option for BC/DR planning - until the introduction of tape pipelining.
Tape pipelining virtually eliminates the impact of latency on the
sustainable throughput of tape backup over distance. With tape pipelining, the
remote tape backup system appears local to the server and is able to sustain
high performance over thousands of miles. This greatly enhanced performance over
distance allows considerable flexibility to companies considering tape as part
of their BC/DR strategy. Tape pipelining can enable a single central site to act
as a backup facility for many geographically dispersed data centers. It can also
enable backup from a central site to a remote site.
Companies can backup stored tape data across low-cost and readily
available IP connections, using both newer native Fibre Channel tape drives as
well as older SCSI drives. In addition, open systems servers such as UNIX and NT
can be incorporated into remote tape strategies.
Many companies are using IP networks for remote disk mirroring which
is typically synchronous and therefore uses substantial network bandwidth during
the day. Since tape backup is typically asynchronous and often done during
nights and weekends, tape pipelining means that businesses can now use their
existing IP networks for both disk mirroring and remote tape backup solutions.
The result is improved data protection and recoverability in the event
of a disaster and a significant reduction in the total cost of ownership of a
remote BC/DR solution.
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Selecting BC/DR Solutions
In planning Business Continuity/Disaster Recovery systems,
businesses can select from a wide range of data protection solutions. The
choices they make will be determined by the importance of the information they
need to protect (i.e. its time sensitivity and business value) and the amount of
money they are willing to spend to protect it. These factors help determine
appropriate the recovery time objective (RTO).
Industry research shows that a typical mid-sized to large enterprise
might have 150 mission- and time-critical applications that require continuous
availability; 300 or so applications that require data restoration within 4 to
24 hours; and 100 or so non-critical applications that can wait as long as
several weeks for data restoration.
Levels of information protection
If a business cannot continue profitable operations without its
data, it usually implements a remote hot site that completely duplicates
critical data and applications and makes them continuously available. The cost
of such a solution is justified by the cost to the business of even a few
minutes of down time. At the other end of the spectrum is business data that may
not need to be restored for days, weeks or even longer after a data center
disruption. In fact, some business data requires no restoration at all but
simply needs to be protected for legal and archival purposes.
The most cost-effective enterprise-wide BC/DR plan will probably
involve a mixture of disk and tape technologies, from the most expensive for
data that needs to be continuously available to less expensive technologies for
data of less time sensitivity and importance. Figure 1 shows what such a plan
might involve. |
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Figure 1. BC/DR plans
typically include a mixture of storage technologies
based on the business
objective of each application. | |
Tape backup market
The evolution toward networked storage, the heightened awareness
of Business Continuity and Disaster Recovery planning and the need to reduce
costs and improve efficiencies throughout IT, is stimulating the market for
cost-effective tape and enterprise backup solutions.
IDC (September
2001) sees the tape market moving from solutions targeting the high end of the
data storage market to lower-cost solutions that add more capacity than
standalone tape drives. Through 2003/2004, as data volumes increase 200%-300%
per year, Meta Group (October 2001) projects that backup/restore windows will be
reduced using intelligent storage, highly parallel tape solutions, and FC-based
SANs.
Gartner Group
states unequivocally (March 2001) that disk-based replication will not replace
tape backup. Tape's low cost - it is about 10 to 60 times less expensive than
disk storage - makes it a compelling economic argument for its inclusion in any
high-availability storage infrastructure.
Tape backup and its historical limitations
Tape backup plays a big role in cost-effective BC/DR systems since it
is significantly less expensive than disk-based replication and is perfectly
appropriate for protecting many types of business information. However,
historically there have been inherent performance problems with tape backup over
distance that limited its role in BC/DR planning.
The primary reason for this limited role is the sequential nature of
tape I/O operations, which makes tape backup highly sensitive to the latency
that accompanies distance. Unlike disk-based operations in which blocks can be
written in parallel, tape I/O for a single block must complete before the next
block can be written. Figure 2 illustrates the typical tape performance falloff
with distance for several popular tape products. As the chart makes plain,
remote tape backup systems simply don't have the throughput to move large
amounts of data over distances of more than a few miles. |
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Figure 2. Tape performance
degrades drastically when distance is increased,
as seen here in a
comparison of several leading tape products. | |
Tape pipelining removes
distance limitations
With tape pipelining technology, tape backup can play a larger role in
BC/DR plans, even at distances of thousands of miles or more.
What is tape pipelining?
Tape pipelining is a data-streaming technique for remote tape
applications. It maximizes the efficient flow of data by using the concepts of
buffering and error recovery, and extending these capabilities over remote
distances via emulation.
How tape pipelining works
In tape pipelining, the server and tape controller can sit
thousands of miles apart, but the two units believe they are sitting next to
each other in the same data center. Both the server and the tape controller have
an intermediate device such as a storage router nearby that emulates the distant
server or tape controller.
The exchange of information between the server and tape controller is
buffered, allowing write/confirm operations to take place in tandem using
temporary memory. For error recovery purposes, operations (and associated data)
in the queue are retained until a successful completion status has been received
from the controller.
Tape pipelining over IP
Figure 3 (below) illustrates usage in a typical IP network. It shows
the dramatically different demands on network bandwidth during the day, versus
nights and weekends. Tape pipelining over IP allows businesses to perform remote
tape backups during those periods when bandwidth is essentially free.
For
example, using existing IP networks between geographically separated facilities,
companies can support their daily production network and real-time synchronous
data replication and disk mirroring applications by day, and perform scheduled,
asynchronous tape backups during evenings and weekends, when excess bandwidth is
available.
Studies show that up to 80 percent of the total costs for a remote
replication solution over five years are network bandwidth costs. Re-using
existing bandwidth rather than maintaining dedicated lines can dramatically
lower overall cost of ownership.
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Figure 3: Periods of low
utilization are ideal for asynchronous disk or tape replication.
With tape
pipelining over IP, the same IP infrastructure can be used for synchronous
disk
mirroring by day and asynchronous tape backup at night when bandwidth is
underutilized. | |
Key benefits of Tape
Pipelining over IP
- Businesses can use existing storage resources and IP networks as part of
their BC/DR solutions by having a central site act as the backup for a number of
geographically dispersed facilities.
- Businesses can streamline server backups into one remote tape backup system
because open systems servers, such as UNIX and NT, can be incorporated into
previously mainframe-only networks.
- Businesses can reuse existing tape drives by incorporating both the newer
native Fibre Channel tape drives as well as older SCSI drives into the remote
tape backup system.
- Businesses can reduce the number of people required by centrally managing
tape backup/restore operations.
- Businesses can use existing IP networks and bandwidth, particularly during
evenings and weekends.
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Remote tape backup - a key
part of BC/DR planning
With support for tape pipelining over IP networks, companies can
perform remote backups using readily available, less expensive IP networks. It
also allows highly distributed organizations to centrally manage the backup
operation for its distributed facilities, improving data availability of its
distributed, mission critical data (Figure 4).
For many companies, analysts recommend that BC/DR plans provide disk
backup (data replication or data mirroring) to secondary backup centers hundreds
of miles from primary sites for critical information that needs to be
continuously available.
Analysts also advise that other types of information be available
within hours of a manmade or natural disaster. The most cost effective way to
meet both needs is to use the same network infrastructure and remote facilities
for both synchronous disk backup (for business information essential to
continuous operations) and for asynchronous tape backup (for less time-critical
but still important data).
Tape pipelining makes it possible by eliminating the latency effects
that traditionally have accompanied tape backup over distance. Devices that make
tape pipelining possible use buffering, emulation and advanced compression
techniques to make local and remote controllers and servers act as if they were
right next to each other.
This not only makes it easier for more businesses to use disk and tape
together to provide maximum coverage for information based on business
requirements and budgetary restrictions, it also allows businesses to take
better advantage of their IP bandwidth.
With tape pipelining, remote tape backup/restore comes of age. For
businesses seeking to improve their data availability while at the same time
controlling costs by using existing hardware, software and network bandwidth,
remote tape backup over IP makes perfect sense. |
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Figure 4. Businesses can now
combine remote disk
and tape backup operations over a single IP network. | |
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