K-ISAM files can be created with their index and data sections on different private disks. Devices, volumes and storage space can be assigned independently to the two parts of the file.
The operands DEVICE, VOLUME and SPACE in the FILE macro apply to the index section, while DDEVICE, DVOLUME and DSPACE apply to the data section. The devices, volumes and spaces are reserved in the same manner. However, the user must remember that specifications for SPACE apply to VOLUME and DEVICE, while specifications for DSPACE apply to DVOLUME and DDEVICE. Only the device types specified for DEVICE may be used in specifications for DDEVICE and there is no default value for DSPACE when a file is created.
If a FILE macro refers to a file which does not yet have storage space reserved, DDEVICE, DVOLUME and DSPACE must always be specified together. For files which already have some storage space, DSPACE may be specified without DDEVICE and DVOLUME. Only the storage space for the entire file may be released (not just for the index section or the data section). Once an ISAM file has been created with the index and data sections on different volumes, it is not possible to move both of these sections to the same volume.
Such separation of the data and index sections of an ISAM file is not possible on public volumes. For reasons of compatibility, NK-ISAM does not reject the operands DDEVICE, DSPACE and DVOLUME, but it ignores them during processing. Due to the optimized buffer management, it is no longer necessary to split the file into separate index and data sections when using NK-ISAM.
The table below contains a list of the equivalent command operands:
Operand in the macro | Operand in the CREATE-FILE and MODIFY-FILE-ATTRIBUTES commands |
|---|---|
DEVICE | DEVICE-TYPE |
VOLUME | VOLUME |
SPACE | SPACE |
DDEVICE | DATA-DEVICE-TYPE |
DVOLUME | DATA-VOLUME |
DSPACE | DATA-SPACE |