The first level-one VIER is created with the VTOC index. Subsequent
VIERs are created whenever a VIER is too full to allow a data set
name to be added to the VTOC index. VIERs have the following characteristics:
- A VIER uses one VIR and contains variable-length index entries.
The number of VIERs in an index depends upon the number of data sets
on the volume.
- All index entries within a VIER are at the same index level. VIERs
in a VTOC index can be on several levels and have a hierarchic relationship.
Index entries in higher-level VIERs point to lower-level VIERs. Index
entries in level-one VIERs (those at the lowest level) point to format-1 or format-8 DSCBs for data sets on the volume.
- Whenever a fourth VIER is created on the same level, a VIER at
a higher level is created. Once a higher-level VIER is filled with
pointers to lower-level VIERs, another VIER at the same level is created.