This subsection explains write and read performance on an OpenTP1 file system during online OpenTP1 operation.

• Write performance on an OpenTP1 file system^#
  
  • When regular Windows files are used
    Data is flushed to disk each time a write operation occurs in order to prevent data loss during Windows delayed write processing. Performance cost is higher when disk flush is performed than when only the write operation is performed.
    
  • When the raw I/O facility is applied
    Performance cost is lower than when regular Windows files are used because flush processing is not needed each time a write operation occurs.
    

  #

  Disk flush processing is not performed when data is written to a file other than an OpenTP1 file system (such as a dclog file).

• Read performance on the OpenTP1 file system
  
  • When regular Windows files are used
    Read processing is performed via the Windows system cache.
    
  • When the raw I/O facility is applied
    Each time a read operation occurs, data is read from the disk.
    
  Read performance is better using regular Windows files than an area to which the raw I/O facility is applied.
  

Note the following about choosing an OpenTP1 file system:

• Unload and backup processing
  Because frequent read operations are involved in loading journal files and backing up OpenTP1 files, the command execution time required to process journal files and to back up files can be reduced to a greater extent when regular Windows files are used than when the raw I/O facility is applied.
  When unloading and backup performance is important, we recommend that you configure the OpenTP1 file system in regular Windows files.
  
• I/O processing during online OpenTP1 operation
  On the following files, write processing occurs more frequently than read processing during online OpenTP1 operation:
  
  • System journal files
  • Checkpoint dump files
  • Status files
  • Server recovery journal files
  • XAR files
  If online performance is important, we recommend that you configure the OpenTP1 file system in an area to which the raw I/O facility is applied.
  
• OpenTP1 restart processing
  Because OpenTP1 restart processing involves considerable data read processing (such as from journal files), you might be able to reduce the restart processing time by using regular Windows files.
  
• Processing in cache blocks
  Performance of the following processing is better when regular Windows files are used than when the raw I/O facility is applied:
  
  • Reading blocks that are not in cache blocks
  • Processing that involves frequent reuse and release of cache blocks
  Performance of the following processing is the same whether regular Windows files are used or the raw I/O facility is applied:
  
  • Reading blocks that are in cache blocks
• I/O processing by the DAM service
  The performance of processing that issues the dc_dam_rewrite function frequently is better when the raw I/O facility is applied than when regular Windows files are used.
  If flush is specified in the dam_update_block_over operand in the DAM service definition, the dc_dam_write function processing involves read processing. If the block specified in the dc_dam_write function is in a cache block, disk read processing does not occur.
  If processing involves frequent reuse and release of cache blocks, write performance is better when the raw I/O facility is applied. Therefore, the performance of dc_dam_write function processing is better when the raw I/O facility is applied than when regular Windows files are used. However, if flush is not specified in the dam_update_block_over operand, performance is better when regular Windows files are used.
  If performance of the dc_dam_write and dc_dam_rewrite functions is important, we recommend that you configure DAM files in an area to which the raw I/O facility is applied. If performance of the dc_dam_read function is important, we recommend that you configure the DAM files in regular Windows files.
  
• I/O processing by the TAM service
  The TAM service performs I/O processing mainly on TAM tables in shared memory. Real I/O processing occurs in TAM files in the following cases:
  
  • Loading TAM tables
  • Unloading TAM tables
  • Real update processing at specific intervals
  • Real update processing when a checkpoint dump is acquired
  In any of these cases, I/O processing is performed asynchronously with user server processing. The user server's TAM access will never wait for I/O processing. Therefore, performance of the dc_tam_read, dc_tam_rewrite, and dc_tam_write functions is the same whether regular Windows files are used or the raw I/O facility is applied.
  

  Note

  The difference in performance between using regular Windows files and when the raw I/O facility is applied also depends on the disk device being used. For some disk devices, there is almost no difference in performance.

Note the following points concerning the OpenTP1 file system in OpenTP1 for Windows:

• Location of OpenTP1 file system
  Do not configure the OpenTP1 file system on a network drive. In order to guarantee disk write processing, configure the OpenTP1 file system on a local disk or a shared disk.
  
• Protection of OpenTP1 files
  Protection of OpenTP1 files is not supported in OpenTP1 for Windows.