A duplicate (snapshot) copy of the file system master index (MI) is kept in memory and periodically written to disk. On system restart, Teradata Database can reconstitute the MI by reading the latest disk copy, rather constructing the MI by reading cylinder indexes (CIs) on each AMP.
The Ferret and Filer utility SCANDISK command has been enhanced to check the validity of the snapshot MI.
- Display the snapshot MI, including the disk location(s) for which the MI was last written
- Validate the structure of the snapshot MI
- Invalidate the snapshot MI to prevent it from being used at the next system restart or Filer invocation
- Speeds most system restarts by eliminating time-consuming step of rebuilding the MI from scratch.
- Similarly, this feature can speed up starting the Filer utility when the database is down or when Filer is started on a FATAL AMP. Filer uses the MI, and having a snapshot to use means Filer often does not need to rebuild the MI.
- Two copies of the snapshot MI are written to disk for redundancy.
- Minor performance impact from periodic writing of MI to disk.
For more information on MI snapshots, see the Filer chapter in Support Utilities.