A modulo designates the number of groups (measured in frames) in the primary file space, as indicated during the creation or reallocation of the file.
The modulo is always an integer remainder in the range 0 to modulo-1. The formula to determine the frame number of the initial frame of the group where the item is located is:
This initial frame number is commonly called the base FID.
The modulo of a file is a critical component of the hashing algorithm access method. It should never be altered in any file-defining item, as this can cause problems such as file inconsistencies.
During the full or account-restore processes, files are resized according to the optional modulo found in the reallocation attribute (attribute 13) of the file-defining item. After changing to the new modulo, all items must be rehashed before they are replaced. This can cause restore processes (also t-load and copy) to run considerably slower.