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Implications of Online BACKUPs?

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The Question is:

What hardware and software combination will allow me to do a backup without
kicking everyone off?

The Answer is :

  The answer to the question depends greatly on the intended results, the
  types of files involved, and the willingness and ability to deal with
  the potential results of any inconsistencies that might arise.
  Tools such as OpenVMS BACKUP permit the ability to acquire backups online,
  though the contents are not synchronized with the I/O caches, nor with any
  application data buffering that might be active.  With /IGNORE=INTERLOCK,
  it is possible to acquire a BACKUP of the disk, but active files may or
  may not be in an entirely consistent state.  (This state is akin to that
  which results from a hard system crash or power failure.)
  Tools such as Oracle Rdb RMU provide the ability to acquire consistent
  BACKUPs of Rdb databases.  As should be obvious, applications can be
  coded to provide support for on-line BACKUPs -- through the use of the
  BACKUP application programming interface, the application can even
  generate the BACKUP saveset.  (Be aware that there is an ECO that should
  be applied for the BACKUP API for OpenVMS V7.1-2 and V7.2.)
  For an entirely consistent BACKUP, all applications and all OpenVMS system
  components referencing the target disk(s) for write should be quiescent,
  or should be entirely shut down.
  BACKUPs using /IGNORE=INTERLOCK -- a qualifier that should be used with
  some caution, as the interlocks are present explicitly to prevent data
  inconsistencies -- can be restored and often manually repaired.  The
  specific repairs that may be required vary, and can include resetting
  the contents of the batch queues (if the restored queue database files
  are in an odd state), or rebuilding or verifying application data files.
  Other techniques -- such as splitting shadowsets and using BACKUP on the
  volume extracted from the shadowset -- are also possible.  This technique
  reduces the window during which the the applications must be quiescent.
  (Splitting the shadowset entirely online is also usually possible, but is
  not supported.)  As with /IGNORE=INTERLOCK, the files may not be in an
  entirely consistent state.
  There may well be hardware that provides some form of physical on-line
  BACKUP capability, but this is outside the realm of the OpenVMS Wizard.
  Better on-line BACKUP support is a current OpenVMS development project.
  Related discussions include topics (1092), (2467), (2512), (2760),
  (3147), (5762), (8371), and likely others.

answer written or last revised on ( 3-FEB-2003 )

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