EHR implementers should anticipate the day when their system is no longer usable because hardware or software components become obsolete. This may occur because hardware replacement parts are not available; the vendor terminates product support; or product features do not stay current with new requirements. System obsolescence is inevitable, so early planning for long term data retention and migration is a necessary protection measure.
 
1.  USE MEDIA WISELY
There are three predominant choices for long term data storage:

• Magnetic tape (10 to 30 years)
• Optical media (100 years)
• Microfilm (300 years)

Each of these media requires some special environmental handling as they are sensitive to contamination from dust and magnetic sources, extreme temperature variations, and high humidity. The more robust the media, the fewer demands for strict environmental controls and less need for 'data refresh' by copying the data to new media.
 
2.  AVOID PROPRIETARY STORAGE TECHNOLOGY. 
The best practice is to avoid using any storage media that relies upon proprietary technology to recover data. Microfilm and optical media (such as CDs, or DVDs) generally avoid such dependence.
 
3. INCREASE THE RETENTION LIFE BY USING WORM TECHNOLOGY.
WORM ('write once read many') is a data storage technology that allows information to be written to storage media a single time, preventing accidentally or intentional alteration or destruction of the data.

4. AVOID PROPRIETARY DATA FORMATS.
Avoid storing data in a format that requires a specific product to read it. Products do become obsolete and vendors do not always provide a backward migration path. Keep data schema simple to avoid issue in reproducing complex databases long after the fact.  Aim for data formats that do not require specialized training to use and understand. Best practice recommends using standard ASCII formats in conjunction with a self describing representation such as XML. Implementers should consider use of the HITSP- endorsed ASTM/HL7 CCD (Continuity of Care Document) standard to store their archival records. Two CDA, Release 2 implementation guides released as draft standards for trial use (DSTU) by HL7 utilize CCD templates: Consult Notes and Operative Notes.

5. SECURE THE ARCHIVED DATA.
It is common practice to archive long term files using archiving service companies. When data goes off-sight and is infrequently used or inspected, best practice recommends encrypting the data using industry standard encryption algorithms to protect confidentiality. In this case, special concern must be given to the method and location of storing the encryption keys to prevent loss, destruction or deterioration. Keys as a loss of the key most likely means that the information will be non-recoverable.

6. DEVELOP DATA ARCHIVING POLICY AND PROCEDURES.
Not all EHR data requires archiving so start with a data retention policy that works for you. If you don't set reasonable parameters for what information to save, how long, and what kind of accessibility is needed, you will find that your data storage requirements will be infinite.
 
Your policy should reflect the value of data being stored. The more valuable it is the more accessible it should be. Your policy should also address retention schedules, technologies, archiving and obsolescence protection. 
  
Resources:

• CCD Quick Start Guide -- from the HIMSS Electronic Health Record Association
• Electronic Data Retention Policy -- SANs publication (2001) that discusses why to have a data retention policy and presents guidelines for what it should cover.
• The National Archives and Records Administration (NARA) Technical Information Paper on the Long-Term Accessibility of Digital-Imaging and Optical Media (1994) for Federal Records.
• WORM Technology -- This article (2005) from Computer Technology Review discusses the difference in WORM tape and drive technologies for long-term data storage.