HP OpenVMS Systems

DFO I/O Transfer Size? (DFG$TRANSFERSIZE)

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The Question is:

 
 
The DFO documentation describes the DFG logical DFG$TRANSFERSIZE as impacting
 DFO's interaction with other pocesses accessing the files but does not provide
 the details of the impact and the relative changes to it's value.  What is the
 impact of larger/sm
aller values for this logical?
 

The Answer is :

 
  The larger the chunks of data transfered by DFO during defragmentation,
  the longer that other access can be locked out.  That said, transfering
  larger chunks of data (up to certain limits) can be more efficient than
  transfering the same volume through more and smaller transfers.  (The
  trade-offs involved are those that are typical of I/O contention, in
  other words.)
 
  The default value of 10,000 is believed an appropriate compromise value
  for most uses and for most configurations.
 

  

     

     
answer written or last revised on ( 11-MAR-2002 )
     
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