To buffer NK4 files, ISAM pools are now also created in units of 4K blocks and not in units of 2K blocks as before. If both NK2 and NK4 files are buffered in an ISAM pool, the ISAM pool will consist of two extents. One to accept 2K blocks and one for 4K blocks. When the ISAM pool is created, the first extent is made available unformatted and as soon as the first file that is buffered via the pool is opened, the extent is created as required for the file (2K or 4K). A second extent is created if a file with some other block control attribute is to be opened via the same ISAM pool. The size of the second extent is also determined by the value specified for the block size.
NK-2K files and NK-4K files should not be processed via the same ISAM pool; otherwise, optimizing the pool size will require double the amount of space, since separate 2K and 4K extents will need to be created in the specified size.