Data back-up is essential, but needs always outstrip capacity. Ian
Murphy looks at the latest solutions
At times, everything done at the corporate level seems to be
designed to make it difficult to ensure accurate and valid
back-ups.
The size both of operating systems and applications has driven
the need for large-scale local storage. Workstations now ship with
disc drives of 40Gbytes or more and even laptops have disc storage
capabilities of over 20Gbytes.
One of the drivers for large local storage capacities is the
number of corporate users with access to the Internet who require
somewhere to cache files and store information. The difficulty of
having so much storage out in the user community is ensuring that
critical information is backed-up.
In the past, tape streamers would have been provided to a small
number of critical workers, but now the user is pointed to a
corporate file server for their data storage and the servers are
automatically backed-up nightly. This is a more secure method of
storage, and responsibility for it lies firmly in the hands of the
IT department.
With local storage and the number of users with laptops on the
increase, recent years have seen a change in this approach.
Mobile users, in particular, have been encouraged to make
regular back-ups of their laptops to their home directory on the
network. Unfortunately, the majority take this to mean "dump the
entire disc to the network", which results in large amounts of
operating system, application and garbage files being stored as
well.
To make matters worse, desktop users who are used to saving data
locally have been encouraged by their line management, often those
with laptops, to do likewise to ensure the safety of critical data.
The result is that huge amounts of storage, often in the region of
terabytes, is wasted. And this hits back-up strategies.
In short, the sheer logistics of moving this amount of data
around is destroying the network infrastructure.
The solution is to move data away from central IT centres and
back out to the departments using local file and print servers.
Careful network design using subnets allows the network
administrator to control the amount of data reaching the backbone
and, by installing back-up solutions inside the servers,
departments can make their own back-ups.
CD-RW
CD-R and CD-RW, while relatively cheap, are only viable for
workstation back-ups of limited amounts of data, while
Magneto-Optical solutions are expensive and rarely seen in most
offices today. This leaves tape technology as the cheaper option,
with the dominant offering still being Dat (Digital Audio Tape)
devices.
Dat
A Dat tape streamer has a respectable back-up capacity of about
40Gbytes per tape, with compression. But the compression
automatically lowers the back-up speed and can increase the
problems of recovery if anything goes wrong. Most Dat drives have a
transfer speed of about 18Gbytes per hour at best.
Digital Linear Tape
The next step up from this is the Digital Linear Tape (DLT)
which is more expensive, both for media and drives. The problem
here is that an autochanger system is a key component for
large-scale server back-up.
Capacity is generally about 80Gbytes per tape, with compression,
and speeds are up to 43Gbytes per hour for single-drive solutions.
Today, DLT accounts for the vast majority of back-up solutions in
regular use, particularly as a server solution, with sales figures
often quoted as up to two million units worldwide.
The problem with DLT is ensuring that tapes are changed
regularly, maintained in the appropriate manner, and removed
off-site securely when the back-up has been completed. In addition,
the capacity of the internal solutions are insufficient to
effectively back-up the local hard drives without tapes being
changed during the back-up process.
NAS
Such responsibility has created a problem for many
ITdepartments, with data being lost. Because of this, network
attached storage (NAS) solutions, such as the ATL Lanvault, or a
standalone DLT library with autochanger, have emerged as the
storage method of choice.
NAS enables departmental solution capable of storing over
200Gbytes, with speeds of about 100Gbytes per hour. However, this
is still below the amount of storage required by the average
department, and the limits of speed and storage using tape
technology have been pushed for some time now.
Tape silos
Tape silos have become increasingly popular with IT departments,
as capacities of several terabytes can be achieved. Many ISPs are
already installing these to protect their customers.
Speed of back-up depends on how the computers and silos are
linked together, but with the emergence of fibre channel and
Gigabit Ethernet, the ability to back-up enterprise data from a
network is finally matching the amount of data in the average
corporate datacentre.
Unfortunately, storage silos are horrendously expensive but,
despite the salesperson telling you that you're nothing without
your data, finding the money to purchase the solution, redesign the
network and implement new procedures is not that easy.
To find a middle ground between large-scale storage solutions
and departmental requirements has always been difficult. However,
recent developments mean that tape capacity and speed are both
increasing. What makes it even more interesting is that the two key
technologies emerging are both competing for the same market, with
major players such as Hewlett-Packard and IBM currently selling
both types of system.
The differentiator is unlikely to be cost, as the solutions are
almost identically priced, nor is capacity or speed likely to play
a major part. The main battle will be multi-supplier development of
a standard versus technology owned and licensed by a single
supplier.
Super DLT
On one side there is Quantum which has made significant
improvements to DLT technology and has launched Super DLT (SDLT).
This technology has been licensed by a number of suppliers,
including HP and IBM.
Quantum produces several different SDLT solutions with storage
capacities of 160-220Gbytes compressed and back-up speeds of
57-115Gbytes per hour. There is a partial guarantee of backward
compatibility of cartridges, depending on the type used. This has a
significant benefit of allowing a migration from existing solutions
to newer technology.
Ultrium
In competition with SDLT, a collaboration between Seagate
Technology, IBM and Hewlett-Packard has resulted in the Ultrium
Format of Linear Tape-Open Technology. Unlike SDLT, which is solely
owned and licensed by Quantum, Ultrium has a number of contributors
which have all produced their own devices.
With previous back-up solutions, changing supplier could mean
that tapes were unreadable, but the Ultrium format consortium is
keen to show that cartridges can be read on all compatible drives -
although there is no qualification process as yet.
Ultrium format cartridges can hold 200Gbytes of data, with a 2:1
compression ratio, and offer back-up speeds of about 100Gbytes per
hour on the HP Surestore Ultrium 230 and 115Gbytes per hour on the
Seagate Viper 200. Both of these solutions can be configured as
both external and internal solutions, making them ideal for
departmental back-up solutions.
Initially, it would appear that SDLT is likely to provide a
smoother path for companies that have already invested in DLT,
especially for IT departments with a large number of sites to
support. Yet, moving forward, the higher capacity of the
entry-level Ultrium devices, allied with the slightly higher speed,
means that the Ultrium format is likely to prove a winner in the
long term.
More on storage can be found at www.itnetwork.com