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Fallback recovery with NGT Recover

Fallback in NGT Recover describes the use of an equivalent or prior image copy when the image copy originally chosen for recovery is not available or is invalid.

In most cases, NGT Recover can fall back to another copy automatically. However, in a few cases where automatic fallback does not occur, it is necessary to restart a failed job.

Note

NGT Recover supports automatic fallback for the following copies:

  • Standard image copies and Instant Snapshot copies

  • Full and incremental copies

  • Copies of table spaces or index spaces

Automatic fallback processing includes the following behavior for NGT Recover:

  • During the ANALYZE phase, if NGT Recover detects that the specified image copy is not available, NGT Recover falls back to an equivalent image copy if one is available. If such an image copy is not available, NGT Recover falls back to an earlier image copy. If no prior image copy is available, NGT Recover tries to recover from the log. If the required log is no longer available, fallback fails and the space is unrecoverable.

  • If the specified image copy is unavailable when NGT Recover attempts to allocate the copy, the recovery falls back to an equivalent image copy. With automatic fallback, NGT Recover uses an earlier image copy or LOAD REPLACE LOG YES or REORG LOG YES log point to recover the space.

  • If the selected image copy is available but is corrupted, NGT Recover does not detect this until after image copy allocation. With automatic fallback, NGT Recover uses an earlier image copy or LOAD REPLACE LOG YES or REORG LOG YES log point to recover the space.

Note

Automatic fallback does not occur if you specify any of the following commands and options:

  • INCOPY option on a RECOVER command

  • RECOVER UNLOADKEYS command

  • REBUILD INDEX command with the WORKDDN option

During automatic fallback, RNGT Recover attempts to recover the specified spaces until all of the spaces are recovered or determined to be unrecoverable. The maximum number of severe errors allowed is defined by the ERRCONT installation option (see ERRCONT=10). The recovery step ends with a completion code of 0 if NGT Recover successfully recovers, initially or following a successful fallback, all of the spaces specified. If NGT Recover cannot recover all of the spaces, the completion code is 12.

Message BMC40227 indicates that NGT Recover is beginning automatic fallback processing. Automatic fallback uses messages BMC40879 to indicate the number of failures before fallback is attempted. For example, the following messages indicate that recovery failed for one space and NGT Recover is beginning automatic fallback processing to recover the space:

BMC40879I 1 OBJECTS WERE NOT RECOVERED DUE TO SEVERE ERRORS

BMC40227I BEGINNING AUTOMATIC FALLBACK

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