Each library can have an optimal blocksize selected at the time it is created.
Starting with tableBASE Version 6, library blocksizes are user-selectable. Previously, blocksize was fixed at 3120 bytes. Starting with Version 6, you can optimize the blocksize for your tables up to the size of a track (or 32,760 bytes, whichever is smaller). This increased flexibility allows you to decrease the time to load tables from the library to a TSR, since fewer I/Os are required. Consider putting all of your large tables together in one library and increasing the blocksize.
Changing the blocksize of a library that has been converted from Version 5 format prohibits it from being converted back to a Version 5 library. Libraries created starting with Version 6 can have any blocksize from 800 to 32760.