UDO vs. Tape for Archival Storage
Introduction
The need for trustworthy, long-term archival storage of important business
information has never been greater. As the volume of digital records grows and
data retention regulations proliferate, organizations are scrambling to
develop long-term data archive strategies that allow them to meet their
corporate and legal obligations, to protect themselves against crippling
litigation and to make the most of their valuable corporate assets. Two of
the most traditional archival storage technologies are magnetic tape and 5.25
inch optical media such as the new 30GB UDO (Ultra Density Optical). Both of
these can be used for archival storage, but the performance
attributes of tape and optical are very different so should be compared in the
context of a professional archive environment.
Archival Storage Criteria
The priorities for a long-term data archive are not the same as those for
online
storage or for backup and disaster recovery applications. When comparing tape
and UDO in high capacity automated libraries, it is necessary to consider those
requirements that are most important for archival storage.
- On-line Storage
- Uninterrupted availability
- High performance read / write access
- Backup and Disaster Recovery
- High media capacity
- High performance read / write streaming
- Low storage cost per GB
- Archival Storage
- Data trustworthiness / authentication
- Extended data longevity
- Rapid read / write random access
- Low Total Cost of Ownership over decades
Tape versus UDO
Tape storage has been designed primarily for backup and disaster recovery
applications. Using tape for data archives is quite common since it provides
professional quality hardware, high performance data streaming and the
flexibility of removable media. However, tape does not offer the same level of
data authentication, media longevity and high performance random access as
UDO. In addition, using tape to store data for decades requires hardware and
media maintenance considerations that can dramatically increase the Total
Cost of Ownership for a tape archive.
Authentication
As with magnetic disk, tape is a rewritable media so does not provide the
same level of audit trail authentication as Write Once optical. UDO uses true
Write Once media that does not allow recorded data to be altered or rewritten.
While some tape products do offer WORM emulation using a hardware lock to
prevent the rewritable tape from being overwritten, this technique is simply not
as secure as a true Write Once media for environments where data
authenticity is paramount.
Media Longevity
Magnetic tape is a very good choice for high capacity, short-term storage
such as backup and disaster recovery, but when used in a long-term archive
additional maintenance considerations come into play. Tape is a relatively
delicate contact media, which degrades with use, can become physically
damaged and is adversely affected by swings in environmental conditions.
Data stored on tape can also be lost from exposure to magnetic fields. In
order to ensure tape data remains available over extended periods of time, it
is strongly recommended that tapes be frequently re-tensioned and data be
periodically refreshed (read and rewritten). Managing re-tension and refresh
cycles for hundreds of tapes written over many years is a complex and costly
task with serious consequences if not managed properly. By contrast, UDO
media is non-magnetic, highly stable, does not degrade with use and does not
demand the extra burden of re-tensioning and refreshing. UDO media has a
greater than 50 year media life, can be stored in a much broader range of
temperatures/humidity and requires virtually zero media maintenance over
decades of active use.
Environmental Specifications UDO 3592 AIT 3 LTO 2
Operating Temperature 5 - 55°C 16 - 32°C 5 - 45°C 10 - 40°C
Operating Relative Humidity 3 - 85% 20 - 80% 20 - 80% 10 - 80%
Archive Temperature -10 - 55°C 16 - 25°C 5 - 32°C 16 - 32°C
Archive Relative Humidity 3 - 90% 20 - 50% 20 - 60% 20 - 80%
Access Performance
Many archive storage environments have a large number of concurrent users
that require access to data within seconds. Tape struggles to meet high data
access service levels because of very slow load and seek times. Tape takes
minutes to access a single random file, whereas UDO can perform the same
task in seconds. Reduced tape performance adds up to slower overall access
cycles, resulting in many fewer possible access cycles per hour. UDO drive in
an automated library can service 5 to 15 times more requests per hour than a
similarly configured tape drive. Environments with many concurrent users will
require more tape drives than optical drives to service the same level of
access pattern frequency. The higher drive to media ratio required in a tape
archive has a very direct and negative impact on the overall system cost.
Drive / Library Specs UDO 3592 AIT 3 LTO 2
Load Time 5 sec 25 sec 10 sec 25 sec
Unload Time 3 sec 15 sec 10 sec 15 sec
Average Seek Time 25 msec 38 sec 27 sec 51 sec
Average Rewind Time 0 sec 38 sec 12 sec 51 sec
Media Exchange Time 6 sec 6 sec 6 sec 6 sec
Average Access Cycle 14 sec 122 sec 65 sec 148 sec
Access Cycles per hour 257 cycles 30 cycles 55 cycles 24 cycles
A single UDO drive provides the following access cycle performance 9x more access cycles than a 3592 tape drive 5x more access cycles than an AIT3 tape drive 11x more access cycles than an LTO2 tape drive.
Total Cost of Ownership
At first glance, the cost per GB for tape storage appears to be extremely low,
but in order to get an accurate picture, it’s necessary to consider the Total
Cost of Ownership for additional hardware, media and administration
essential to a long-term tape archive. A tape archive will require more drives
than a UDO archive to achieve the same level of level of access cycle
performance. Additional tape media is required each time data is refreshed,
and for redundant media copies made for insurance against physical tape
damage. Significant additional administration and drive resource is also
needed for managing a re-tension and refresh programme in order to ensure
that data written to tape remains accessible. Adding up the additional
hardware, media and administration costs results in a much higher TCO for
tape archives than first imagined. Not only does UDO offer a very competitive
TCO when compared to tape in a long-term archive, it does so with greater
authentication, faster access performance and much simpler media
management.
Summary
To properly compare technologies, they need to be put in context. Tape has
many strong qualities that make it an ideal backup and disaster recovery
technology, but to use it in a long-term archival storage environment demands
a number of performance and economic trade-offs. By contrast, UDO was
designed specifically for archival storage so meets the technical and
economic requirements of a professional archive strategy.
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