HP OpenVMS Systems

Does a lack of errors really mean no errors?

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The Question is:

 
I recently aquired several 'spare' disks that will be
used for standalone backups.  In the past I had always
sent the output to a backup saveset on a tape device.
 
In my first attempt at a disk-to-disk backup
 
     $ BACKUP/IMAGE/VERIFY  DIA0:  DIA12:
 
the backup completed successfully
 
     $ %BACKUP-I-PROCDONE, Operation completed......
 
but, there was no message for the verification
 
     $ %BACKUP-I-STARTVERIFY, starting verification pass
 
??????????
 
The output disk 'appears' to be OK, but I am concerned about
the lack of a verification message.
 
Is the disk-to-disk verification done silently??
 
 

The Answer is :

  With few exceptions, the general rule in DCL is to succeed silently but
  to issue a message if there is a failure or warning condition. The HELP
  text for the /VERIFY confirms this behaviour:
 
BACKUP
 
  /VERIFY
 
     Command Qualifier
 
     Specifies that the contents of the output specifier be compared
     with the contents of the input specifier after a save, restore,
     or copy operation is completed. If a file does not compare
     successfully, BACKUP displays an error message.
 
 
  When performing a backup to TAPE, being a sequential access medium,
  verification can only be done by rewinding the tape. Since this would
  be result in severe performance degradation if it were done file by file,
  BACKUP does it as a separate pass. Since disk devices are random access,
  in some cases BACKUP will do both the copy and verification file by file,
  so there is no verification pass as such, hence the lack of any message.
 
  Note: The wizard is unable to identify for certain the exact circumstances
  under which backup will choose to perform verification file by file or
  as a seperate pass. In a few experiments performed here on OpenVMS/Alpha
  and OpenVMS/VAX V6.2 on RZ29 disks served from an HSD10 controller, the
  verifications were performed as a separate pass, with a BACKUP-I-STARTVERIFY
  message. However the wizard has also performed disk to disk image backups
  where the verification was performed file by file. It probably has something
  to do with the disk type.
 
  If you really want to SEE that the verify is being performed, add the /LOG
  qualifier to your BACKUP command.
 

  

     

     
answer written or last revised on ( 12-MAY-1999 )
     
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