Expanding the Size of a Shadow
From InterBase
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If a database is expected to increase in size, or if the database is already larger than the space available for a shadow on one disk, you might need to expand the size of the shadow. To do this, drop the current shadow and create a new one containing additional files. To add a shadow file, first use DROP SHADOW to delete the existing shadow, then use CREATE SHADOW to recreate it with the desired number of secondary files.
The page length allocated for secondary shadow files need not correspond to the page length of the database’s secondary files. As the database grows and its first shadow file becomes full, updates to the database automatically overflow into the next shadow file.