Minnesota  State Archives

Electronic Records Management Guidelines

Digital Media


On-going and rapid advances in technology dictate that you store your electronic records on media that enable you to meet your long-term operational and legal requirements. Legally, your records must be trustworthy, complete, accessible, legally admissible in court, and durable for as long as you need them. Because every digital storage option will eventually become obsolete, consider digital storage options that will enable you to maintain records by migrating and/or converting them during their required retention period.

Legal Framework
For more information on the legal framework you must consider when selecting digital storage media refer to the Legal Framework chapter of these guidelines and the Minnesota State Archives’ Preserving and Disposing of Government Records.


Key Concepts

Before you determine which digital media will meet your long-term legal and operational needs, familiarize yourself with the following key concepts:


Digital Media

Digital data is stored on digital media. Digital media can be divided into three main types:

  • Magnetic. On magnetic media, the digital data is encoded as microscopic magnetized needles on the surface of the medium (e.g., tape).
  • Optical. On optical media, the digital data is encoded by creating microscopic holes in the surface of the medium (e.g., CD or DVD).
  • Solid State.  Containing no moving parts, solid state media encode digital data by applying small voltages of electricity that temporarily induced a group of transistors either on or off.  (e.g., flash memory cards, USB removable media). 

Based on the characteristics of the different types of media, access to the information is divided into two categories, sequential and random access. 

  • Sequential. Sequential access requires the user to access specific information by accessing the preceding information on the medium. For example, if you want to view a specific portion of magnetic tape, you must first fast-forward through the preceding portion of the tape.
  • Random. Some digital media allow users to access the stored information from any physical place on the media. For example, when you connect a flash drive to your computer or insert a DVD, you can access any single file stored on the media without having to first access all the files that precede it.

When choosing a media one must also consider the purpose for storing the data.  How long will the records need to be accessible?  Who will need to access the files?  Are there are legal requirements associated with ensuring the authenticity of the records?  If so, Write-Once Read-Many (WORM) technology should be considered.  WORM technology originally was an optical media option.  It required a special WORM disk drive to enable the user to read or write to specific WORM disks.  Today, WORM technology is also available to use with magnetic media, for a lower price with a higher capacity.  As long as the machine can recognized WORM tapes, there is no need for a separate tape drive.   


Magnetic Media

Magnetic media includes:

Magnetic Disk. Magnetic disks include the hard disk found in your computer that stores the programs and files you work with daily. Magnetic disks provide random access. Also included are:

  • External Hard Drive.  External hard drives are encased in housing and connected via cable to a computer port. 
  • Network Environment.  Multiple hard drives are connected to each other in a way that shares resources and information, creating a network.

Magnetic Tape. Magnetic tapes come in reel-to-reel, as well as cartridge format (encased in housing for ease of use). The two main advantages of magnetic tapes are their relatively low cost and their large storage capacities. Magnetic tapes provide sequential access to stored information, which is slower than the random access of magnetic disks. Magnetic tapes are a common choice for long-term storage or the transport of large volumes of information.  WORM technology is available with many of these tape formats.  The only requirement is that the machine is capable of recognizing the special WORM tape.    As an example, Linear Tape-Open (LTO) is an open-standard magnetic take system that allows interoperability between tapes and tape drives made by different manufacturers.


Optical Media

Optical media options include:

Compact Disk (CD). Compact disks come in a variety of formats. These formats include CD-ROMs that are read-only, CD-Rs that you can write to once and are then read-only, and CD-RWs that you can read and write to in multiple sessions.  CD-RWs have less life expectancy than non-rewritable disks.  CDs are relatively stable and with proper error checking suitable for data storage of five years before refreshing. 

Standard Definition Digital Versatile Disk (SD-DVD/DVD). These disks are also called digital video disks, but do not necessarily include video. DVD disks have more storage capacity than CD-ROMs.  DVDs come in various types +/- and may or may not be compatible with each other (see list below).  When DVDs players and recorders were first developed they would only play the + or – formats, not both.  Today, however, most DVD recorders and players will accept either the +/- format.  The life expectancy of DVDs are similar to that of CDs but with the ever changing technology, may not be the most reliable storage medium for long-term files. Common types of DVDs include:

  • DVD+R and DVD-R.  DVD+R and DVD-Rs can be written to once and then are read only. (4.7 GB per layer)  DVD-Rs are more commonly compatible with older machines; DVD+Rs were only officially recognized as an official DVD format in 2008. 
  • DVD-RAM. These DVDs are rewritable disks with exceptional storage capacity.  They come in one- or two-sided formats. Rewritable disks have less life expectancy that non-rewritable ones.
  • DVD+RW and DVD-RW. These are direct competitors to DVD-RAM with similar functionality, are rewritable and have slightly greater storage capacity.

Write-Once, Read-Many (WORM) disk. WORM disks require a specific WORM disk drive to enable the user to write or read the disk. WORM disks function the same as CD-R and DVD-R disks. 

High-Definition DVD. Envisioned to be the successor of standard definition DVDs.  High-definition DVDs have higher storage capacity than a standard definition DVD.  A single sided HD-DVD can store 25 GB rather than the 4.7 of a SD-DVD.  The optical technology uses a blue ray (rather than a red ray) which has a shorter wavelength which increases the storage capacity of the disks.  Blu-Ray and HD-DVD were two competing formats. Support for HD-DVD was discontinued in early 2008.    

  • Blu-ray Disc.  Developed by the Blu-Ray Disc Association, the main uses for this disk are for video, computer games and data storage.    BD-R and BD-RE are the read-only and rewriteable formats of the Blu-ray disc. 
  • HD-DVD.  Supported by Toshiba.  A competitor of Blu-Ray, that also offered higher storage capacity than previous DVD formats.  Support for HD –DVD +/- Rwas discontinued in early 2008, making Blu-ray the format of choice for higher capacity optical storage.

Optical cards. Optical cards, also known as “smart cards,” are the size of a credit card. They come in read-only and read-write formats. They are not in widespread use except for limited applications, such as automatic teller machines, personal identification for security systems, and airline reservations.

Optical tape. Optical tape is tape coated with optical recording material. Optical tape is not widely used.


Solid State Media

Solid state media is used in various removable devices utilizing flash memory including digital cameras, cell phones, computer games, music players, and video recorders.   Small cards and “memory sticks” store images, games, music, data, programs, and video.  Storage capacities of these cards or sticks are ever increasing; when they were originally introduced their size was between 32 MB and 512 MB; there are now models that can store over a terabyte. 

Memory cards and flash drives (memory sticks) can be connected to a computer via card reader or USB port to assist with data transfer between devices.  The small size, portability, and no moving parts make solid state media attractive.   Data is accessed randomly.  All formats are re-writable.  Long-term storage capabilities of solid state technology are still being studied.     Some examples of solid state media are listed below. 

  • Flash Memory Cards.  Memory cards are made in a variety of sizes and range from around an inch square to around a centimeter long.  Larger cards are often used in digital cameras and smaller cards in cell phones. There is a great variety of card types in use as well as the storage size of the cards. 
  • USB Flash Drives.  Connected to a computer via a USB port, these ‘drives’ (storage devices) are a very portable option for data transfer.   
  • Solid State Hard Drives.  Uses solid state memory to store data, with more capacity than memory cards and flash drives.  The drives have no moving parts which are an advantage, but the cost per GB is currently more than with an external hard drive. 


Digital Media Capacity

As indicated above, various types of media store different amounts of data.  Storage capacity and file size is measured in bytes, the basic unit of measurement. 

  • 1,024 bytes make a kilobyte (KB)
  • 1,024 KBs make a megabyte (MB)
  • 1,024 MBs make a gigabyte (GB)
  • 1,024 GBs make a terabyte (TB) 
  • 1,024 TBs make a petabyte (PB)

To put things in perspective, a one page Word document may be only 27 KB; a 75 page document is 425 KB; and a Word document with images may be 20 MB.  A single photograph, depending on size and quality, can range from less than 5 KB to 30 MB and higher.  To best determine what media you would like to store files on, you will need to understand the amount of storage you need now as well as in the future.  This will help determine which storage option is the best for you. 


Media Life Expectancy

All digital media has finite life spans which are dependent on a number of factors, including manufacturing quality, age and condition before recording, handling and maintenance, frequency of access, and storage conditions.  Studies have indicated that under optimal conditions, the life expectancy of magnetic media ranges from 10 to 20 years for different types, while optical media may last as long as 30 years.  However, in real life situations, most media life expectancies are significantly less.


Care and Handling of Digital Media

To help make your digital media last as long as possible, follow the guidelines below.  This list is not complete, as each media type will have its own requirements for proper handling. 

All Media

  • Purchase and use high quality storage media. Batch test new media to validate manufacturing quality.
  • Read a statistical sample (3% minimum) of recorded media annually to identify and correct any loss of data. Re-copy batch if errors appear.
  • Prohibit smoking and eating in areas where digital media are stored and also in media test or evaluation areas.
  • Maintain media in storage areas that are dust-free and controlled for temperature and humidity.
  • Open a recordable media package only when ready to record.

Magnetic Media

  • Wind and rewind magnetic media before recording.
  • Every three to four years — or more frequently if you read them often — rewind each tape under controlled tension.
  • Before they are five years old, re-copy tapes onto new and/or updated tapes.
  • Minimize handling and avoid touching the media surface or edges.

Optical Media

  • Do not touch or mark the data side of the disk surface. Handle disks by the outer edge or center hole.
  • Be careful not to damage the label side of the disk. Do not apply or attempt to reposition adhesive labels. Do not write on disk with pen, pencil, or fine tip marker. Use only non-solvent based felt tip permanent marker.
  • Check disk for damage or contamination after each use. Clean only when surface contamination is visible by wiping the disk from the center out in a radial motion with an anti-static cloth. 
  • Depending on use and storage conditions, CDs and DVDs should be re-copied every five years or sooner.

Solid State Media

  • Be careful not to get the media wet.
  • Because of the small and portable nature of many flash drives and memory cards, be careful to not lose or misplace the media.
  • Be careful with inserting the card into a card reader or flash drive into the USB port.  Use your computers ‘Disconnect Safely’ tool when finished. 
  • Do not expose to great temperature fluctuations.


Storage Options

As part of a records management plan for electronic records, you will need to determine where and how these records will be stored.  This decision will be based on the likelihood of access of those resources versus the overall cost in maintaining them.  Your options for storage include online, near-line, and offline. 

Online:  Records stored online are continually accessible via a network.  Records are located on a hard drive or networked server.  This option maintains the greatest functionality but requires more expensive network storage. 

Near-line: Records stored in a near-line environment are stored on removable media such as on an optical disk or magnetic tape.  Files can be accessed via the network, but are not physically on the network (e.g., an optical media jukebox).  This option maintains a moderate amount of functionality.  While the storage space is cheaper than online storage, near-line storage requires that the user take time to manipulate both the files and media of choice to access the records. 

Offline:  Records stored offline are stored on removable media that is not accessible through a network.  Files must be physically retrieved from the digital media itself, such as on an external hard drive or magnetic tape.  This option trades functionality for stability, but maintains records in a digital format.  

For more information on storage procedures and facility requirements please see the Digital Media Storage chapter of these guidelines.  


Performance Issues to Consider

As you discuss your digital media options, consider each option’s performance characteristics in terms of your records management needs.

Planning.  In addition to choosing a storage medium, you should establish procedures to refresh your digital stored records periodically.  Refreshing digital media occurs when you copy stored data from old to new digital media.  To verify that there was no loss of content or that the content was not changed during the transfer, perform integrity checks (such as a checksum) on the content both before and after the process. 

Speed of access. When selecting a digital storage medium, consider how quickly you or authorized members of the public may need to access your records. You may find that some types of records require fast access, while others do not. For example, you may need fast access to key policy decisions, but not to employee records.

Capacity. The volume of records that you can store on the medium will be a key consideration. Examine the volume of the records you now store, and try to determine what your needs may be in the future. Consider the official definition of a record and whether that definition will affect the records volume that you need to manage.

Longevity. Research how long the industry will support various media options and compare those figures with the time period that you need to keep your records according to the approved records retention schedule. You may find a medium that meets all your needs, but is not widely used or has a high risk of becoming obsolete, thereby limiting its usefulness in the future.

Durability. Research how easily a given medium can be damaged or will deteriorate. You may find that a medium that deteriorates after three years will still be a suitable option for records that need to be retained for only one year. Be sure to review your records retention periods.

Portability. Determine how portable your stored records should be. Some media, such as flash drives and DVDs are very portable. Consider who will be accessing your records. For example, will the public, the press, or other agencies frequently access your records?  You should also consider whether you or anyone accessing the records will need special devices to read the records. What equipment will be necessary to view the files?

Compatibility. Assess the backward and forward compatibility of the digital media you are considering. For example, DVD drives are backward-compatible for CDs, but a CD drive is not forward-compatible for DVDs. This discussion will help you to determine how often you may need to upgrade supporting computer systems, migrate records, and/or convert records.

Cost. Assess the costs and benefits of each medium you consider. What will the medium itself cost as well as the equipment required to create and view it?  Be sure to discuss the costs of converting and/or migrating records, as well as the basic costs of the system.


Key Issues to Consider

Now that you are familiar with some of the basic concepts and options of digital storage media, you can use the questions below to discuss how those concepts relate to your agency.

Pay special attention to the questions posed by the legal framework, including the required records retention periods. Examine your current and future records series. Some records series may require large storage capacities, may need to be retained for a long time, or may be frequently accessed by the public, other agencies, or other groups. Prioritizing your needs in light of the legal requirements will help you narrow your discussion and focus your research.

The point is to determine the best option for your agency that meets your legal and operational needs, not merely to automatically upgrade technology. For example, if you are currently using magnetic tape, you may discover that magnetic tape remains your best choice.


Discussion Questions

  • What types of records do we need to store (e.g., graphics, text, database text)? What file formats? How large are our record files?
  • Which performance issues are most important in our situation?
  • How long do we need to retain the records?
  • How often will we need to access the records?
  • Will all records or specific records series be frequently accessed by the public or other groups?
  • How well does our current media meet our needs? What costs would be incurred for supplies, equipment, and training that would be required if we were to switch to or add a new storage medium?
  • Are any of the media that we use or are considering expected to become obsolete in the near future? Will the medium, as well as the necessary hardware and software, still be available from a number of suppliers for as long as we need? Has the developer defined a migration path for improved versions of the medium?



Digital Media, Annotated List of Resources  go to Annotated list of resources

Next Chapter, Digital Media Storage  go to Annotated list of resources


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Electronic Records Management Guidelines, March 2012, Version 5.

Links verified March 13, 2012.