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Main Page > AA638 A8/A12
What is SSMDF?

What is SSMDF?

SSMDF is a specialized data format used by the Archive Appliance when writing to UDO media. SSMDF provides enhanced performance and data recoverability over other removeable media formats.  It contains an ECMA standard volume header to allow the media to be easily identified.  Both file metadata (i.e. the information that describes the file data) and the file data are written to the media so that a complete data recovery can be done from the UDO media, if needed.  When the Archive Appliance fills and closes a piece of UDO media, it writes an FRI (Fast Recovery Index) on the media to provide fast recovery of both metadata and data in the event of a full data recovery situation. 

 

 

Why was it Chosen?

 There are several key criteria when choosing a media format for an archive system:

  • Media utilization
    • SSMDF is more space efficient, especially with small files which can be packed into a single 8K UDO sector.  UDF has 3 sectors of overhead per file, making it extremely inefficient for smaller files.  UDF also requires additional overhead to track large files.
  • Read and write performance
    • SSMDF writes to UDO media sequentially, eliminating seek overhead and facilitating faster streaming performance.  UDF format requires extensive use of seek during write operations and thereby creates performance inefficiencies. 
    • UDF is inefficient for reading due to the need to issue multiple reads for file overhead before reading the file data.
  • Scalability to large file counts and large file sizes
    • SSMDF has enhanced features that are capable of tracking large files that span media without restriction.
  • Recoverability
    • SSMDF is self describing and enhances recovery of file data from media with the addition of the File Recovery Index (FRI).  This significantly speeds up recoverability where UDF would have to sequentially read through the complete media to recovery the files. 
    • SSMDF provides tracking of file renames and deletes so its recovery is much more complete.
    • SSMDF supports and facilitates file versioning. 
Article ID: 10494 Article Created: 11-04-2013 14:29 PMLast Modified: 11-04-2013 14:29 PM

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