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VERS STORY | STANDARD | ASSESSMENT | PROJECTS | DIGITAL ARCHIVE | TRAINING | TOOLKIT | PUBLICATIONS | |
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4.0 Physical Storage Media 1
4.1 Recommendations
for Small Agencies The physical storage of electronic records is as important as the long term digital format of the records themselves. VEOs must be stored on media which is relatively long lasting, has a reasonably high capacity and which is widely supported by storage media vendors. In order to protect against media obsolescence, deterioration or for transfer, media must be refreshed periodically. Refreshing is the process of physically copying records from one piece of media to another. The process of refreshing can be made entirely automatic. This Standard recommends the use of a small range of types of magnetic tape, which PROV believe encompasses the needs of small to large agencies. Magnetic tape is the preferred medium because of high densities, high capacities, reliability, industry acceptance and independence from vendor file systems. For smaller agencies, CD-ROM and successor technology may be suitable because of lower volumes, and cost constraints. For transfers to other agencies or to PROV, the use of the Internet is recommended, but if this is not viable or not feasible (due to, say, security issues), then a range of tapes and removable discs is suggested. All storage systems should store at least two copies of each of the records, and PROV recommends adopting different storage technologies for the primary and secondary copies. This reduces the chance of data loss due to a bad manufacturing batch, or problems with the readers. PROV particularly cautions against adopting systems that use new technology. New technology is often attractive as it promises high capacity at a lower cost than existing technology. Unfortunately, the history of computer storage is littered with new technology that either did not live up to its initial promise (particularly with regard to reliability), or quickly went out of production due to the failure of the company that developed it. In addition PROV recommends care in selecting components so that selection of one particular component (media type, data storage management software, host operating system or host hardware) does not force the selection of the other components. A good data storage system should be flexible and handle many components.
4.1 Recommendations for Small AgenciesFor agencies that generate up to 10 Gigabytes of data annually, PROV recommends storage on either Travan magnetic tapes, writable CDs, or Zip drives. At the low end, a manual data storage system would be around $1000, but it should be noted that this system would require manual loading and unloading of media and would consequently have a relatively high running cost. Purchase of a small CD-R jukebox (robot) would avoid this manual handling and would cost between $10,000 and $30,000 depending on capacity.
4.2 Recommendations for Medium AgenciesFor agencies that generate between 10 Gigabytes and 1.5 Terabytes of data annually, PROV recommends storage on Quantum DLT drives. Normal data storage practice is to store two independent copies, so this translates to between 20 Gigabytes and 3 Terabytes of storage annually. The expected cost of such a system would be around $44,000 capital cost and around $16,000 per annum consumables. This figure comprises two drives (around $12,000 each), a robot (around $20,000). This costing does not include staff costs. These would be between 0.5 and 1.0 effective full time positions.
4.3 Recommendations for Large AgenciesFor agencies that generate over 1.5 Terabytes of data annually, PROV recommends storage on 3490E/Timberline drives with 9840 drives for the second copy. PROV also recommends that at least two independent copies be made of data on separate media technologies. This means that the actual increase in storage is twice the amount of data generated. The expected cost of such a system would be around $700,000 capital cost and around $10,000 per Terabyte of data stored in the system annually. This figure would buy a large silo (e.g. a StorageTek silo) and associated drives. Staff costs would be between 1 and 2 effective full time positions. Because these systems are very widely used for data storage, they can be connected to a very wide range of host machines running a range of operating systems.
4.4 Recommendations for Transfer FormatsPROV may accept transfer of records from an agency by means of the Internet in the future. However, at present, PROV will accept only a limited set of media formats:
4.5 Recommendations for the FutureIt is strongly recommended that any agency implementing a data storage system should obtain expert assistance in
Endnotes1. For a more detailed discussion of physical storage media see Appendix Four: Digital Storage Media for VERS | |||||
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