Saving your assets: Storage issues loom large as data maintains its value longer.

31 Oct, 2003 By: Michael Dakan

In our annual review of trends and developments in the AEC software industry (Cadalyst, August 2003), we discussed the growing emphasis on BIM, or building information modeling. As BIM products and methods mature and become more ubiquitous, they will require changes in office policies and procedures, many of which fall under the purview of the CAD manager.

Among these changes are the requirements for additional training and support for CAD tools and improved short- and long-term methods of data storage and retrieval. The requirements for data storage have been on an exponential curve upward for a long time, and this trend will continue. An interesting study done by the University of California, Berkeley, a couple of years ago estimated annual data generation worldwide to be over 1.5 exabytes, with an annual growth rate of 50% ( how-much-info/index.html). An exabyte is a billion gigabytes, well beyond comprehension for most of us. Some of this data may be used only temporarily and then discarded, but a lot of it must be stored and tracked for some period of time.

Technological advances in storage capacity have kept up pretty well with the increased data requirements. In design offices, the result is that storage capacity that used to be calculated in the hundreds and thousands of megabytes is now measured in the hundreds and thousands of gigabytes. It won't be long before everyone is thinking of online storage in terms of thousands of terabytes (a terabyte is thousands of gigabytes). The problem is not so much the technology needed to keep up with the volume of storage demands as it is the more human problem of keeping track of what is stored and retrieving just what you need in the future.

If BIM delivers on its promises, CAD data will continue to become increasingly valuable and its life expectancy will increase. Data that is currently most useful during the limited period of building design and construction will be useful for the entire thirty- to fifty-year, or longer, lifecycle of a building. This means that design offices will likely have to take on increased responsibilities to ensure that the data is well maintained and usable for a longer period of time.


Data archiving serves a variety of needs and uses, ranging from daily backups and working file copies to business and legal record requirements of completed work and contract obligations. Daily backup may be the responsibility of a separate IT or network administration department in larger organizations, but other kinds of project archiving needs often fall to the CAD manager.

Almost every design firm has suffered data losses because of user file management errors, virus problems, and occasional workstation hard-drive crashes. Though this can be irritating and result in some lost effort and productivity, most organizations have a functioning daily backup system that minimizes these losses. Usually, these systems feature a tape drive with capacities adequate to back up working data files so that a user seldom can permanently lose more than a few hours of work.

Though tape systems generally do an excellent job of protecting against short-term losses, they aren't as satisfactory for long-term archiving. Daily backups are indiscriminate-they simply make a copy of everything that is on a hard drive, or within a specific set of folders. There is no attempt to sort out file redundancies or outdated, corrupt, and infected files. This can make later retrieval of the correct version of the most recent good file tedious and difficult.


Magnetic media. Data stored on magnetic media is inherently volatile and vulnerable to deterioration. Even though most firms try to maintain good, safe off-site storage procedures, there is no way to entirely eliminate transient electromagnetism around the Earth and the cosmic radiation that constantly bombards us. This can lead to long-term data degradation. Because the recording and retrieval process relies on moving the tape over magnetic heads, the tape is subject to mechanical failure such as breaking, stretching, and head wear. The reliable life expectancy of magnetic storage media is constantly improving, and DLT-format cartridge manufacturers claim a thirty-year life. For daily and monthly backup purposes, magnetic tape is convenient, retrieval times are adequate, and the data stability of the magnetic media is well within the needed life expectancy.

Optical media. For longer-term archival storage, optical storage media provide longer life expectancy and stability. Optical media have an almost unlimited storage life. Optical write-once technology typically uses a metallic coating of some sort on glass or plastic disks to receive laser burning, and this coating can be subject to long-term environmental degradation from pollution in the air and mechanical damage from abrasion and scratching. When properly stored and protected, though, optical media should have a life expectancy that exceeds just about any archiving need.

Writable CD-ROMs have been used for a number of years for things such as project archiving and record sets at the end of phases, but the limited capacity of a CD-ROM (typically 700MB or less) makes writing CD-ROMs a fairly tedious task if you need more than one disk to hold a complete project archive. Now that writable DVD drives and media (4.7GB data capacity) are commonplace and the data format is fairly standardized, this has become a popular choice for all sorts of project archiving.

DVDs are a popular choice for all sorts of project archiving. Larger capacities in DVD formats are also becoming available. The formats have not yet been standardized, though, so using higher capacity DVDs is risky in terms of future compatibility.


Standard, long-lived data formats are an important consideration. For instance, most companies have probably changed the type and format of their tape backup systems over the past five or ten years, sometimes more than once, in the neverending search for higher capacities and speed. Therefore, many companies have data cartridges in storage for which they no longer have tape drives on-line. Also, most tape backup software uses a tape cataloging system and file compression of some sort to maximize storage capacity, so you may have to use proprietary software that is no longer in development as well as an old drive to recover the information on a tape. If you stick with industry- standard storage types and file formats, you'll have a better chance of recovering the data on older storage media for a longer period of time.

Design offices usually need to keep data in original CAD file formats for legal records and for future design service opportunities over the life of a building. You may also want to keep archive copies in other file formats for "working" sets of project data. These sets can be disseminated to a variety of different entities over time to satisfy different information needs about a building project.

Many companies outside the design professions are standardizing on Adobe Acrobat files (PDFs) for long-term archiving. Recent advances in the software used to create PDFs make them better suited for viewing and working with CAD drawings as well as other types of project information (Cadalyst, October 2003, p. 18). Files created specifically for viewing drawings on the Web-those in Autodesk's DWF format, for example-are also increasingly in use.

Regardless of physical storage methods and file formats used, it's becoming increasingly clear that electronic files are the lifeblood of most building design firms, and represent a major asset. Electronic data is increasingly valuable both to design professionals and to building owners and managers, and it may become a major source of continuing future revenue for design firms. CAD managers, along with general IT workers, will need to devote an increasing amount of time and energy to maintaining data and making sure it is available and accessible for a long time.

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