HP OpenVMS Systems

Shadowing and Forced Errors? (Bad Blocks)

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The Question is:

 
What exactly does the MOUNT qualifier /OVERRIDE=NO_FORCED_ERROR do?  Will using
 this qualifier allow me to make a shadow set using disks that have the NOFE
 characteristic? (The volume shadowing SPD implies that such disks _can_ be
 used but that "features
are restricted")  What are the consequences of using this qualifier to make a
 shadow set using NOFE disks?  Thank you.
 
 

The Answer is :

 
  From the HELP text:
 
     NO_FORCED_ERROR
 
                    Directs the Mount command to proceed with
                    shadowing, even though the device or controller
                    does not support forced error handling. Using
                    unsupported SCSI disks can cause members to
                    be removed from a shadow set if certain error
                    conditions arise that cannot be corrected, because
                    some SCSI disks do not implement READL and WRITEL
                    commands that support disk bad block repair.
 
 
 
  In other words, your shadowset volumes can expel member disk volumes
  on incidents of unrecoverable errors, rather than first attempting
  to correct the errors on the volume.
 
  Assume a two-member shadowset DSA1:, consisting of DKA100: and DKA200:.
  Further assume that DKA200: has a sector-level error.  If shadowset
  reads (as it should) data from both DKA100: and DKA200:, the shadowset
  will receive an error reading the failing sector on DKA200: and will
  initiate a bad block revectoring operation.  The correct data from
  DKA100: will be written to the revectored sector on DKA200:.
 
  If your disk volume does not have forced-error support or if the
  shadowset is running with errors in each copy of the sector (eg:
  one member shadowset), then the sector-level disk errors will cause
  the member volume to be ejected from the shadowset.
 
  For details on the SCSI READL and WRITEL commands and their function,
  please see the READ LONG and WRITE LONG command details within the
  SCSI specifications.
 
  For information on OpenVMS bad block handling, please see topic (6926).
 
  The OpenVMS Wizard cannot and does not recommend using disk drives
  that do not support forced error handling.
 

  

     

     
answer written or last revised on ( 25-JUN-2003 )
     
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