Before Creating a Shadow
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Before creating a shadow, consider the following questions:
- Where will the shadow reside?
A shadow should be created on a different disk from where the main database resides. Because shadowing is intended as a recovery mechanism in case of disk failure, maintaining a database and its shadow on the same disk defeats the purpose of shadowing.
- How will the shadow be distributed?
A shadow can be created as a single disk file called a shadow file or as multiple files called a shadow set. To improve space allocation and disk I/O, each file in a shadow set can be placed on a different disk.
- If something happens that makes a shadow unavailable, should users be allowed to access the database?
If a shadow becomes unavailable, InterBase can either deny user access until shadowing is resumed, or InterBase can allow access even though database changes are not being shadowed. Depending on which database behavior is desired, the database administrator (DBA) creates a shadow either in auto mode or in manual mode. For more information about these modes, see Auto Mode and Manual Mode (Using CREATE SHADOW).
- If a shadow takes over for a database, should a new shadow be automatically created?
To ensure that a new shadow is automatically created, create a conditional shadow. For more information, see Conditional Shadows.