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DELTA ANALYSIS

By comparing the current version of a file to a previous copy, it is possible to determine which portions of a file have changed, and then send only those changes. The problems with these techniques (we'll call them "delta analysis") are:

• You need to reserve as much free disk space as the size of the files you are backing up so that a local copy of all your files can be stored for comparison (in addition to the free space you need to compress all the data before it's transmitted)
  

• The CPU overhead to find the file changes can be significant. In some cases, it will take longer to perform a delta analysis than it would take to just compress and send the entire file each time.
  

• If a file is newly created or if a file has not changed for a while, there may not be a previous copy to compare it against. In most of these cases, the delta analysis will then not provide any benefit at all.
  

• Maintaining local file caches, performing the analysis and rebuilding the file at the remote end to its original format can be a very complex process that would be more prone to errors and failures.
  

• The level of security (protection of your data) is reduced since your data will now exist unencrypted on the remote server for at least a period of time in order for the delta process to work.
  

• Configuring and fine tuning these types of systems will require more effort and trial and error.
  

• Depending on what parts of a file are changed or how much of a file is changed, a delta analysis may not be able to effectively determine what changes were made to the file and would then have to back up the entire file.
  
   

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