SVC 021
SVC 021 is a Type 3 SVC that is issued by the STOW macro. This macro does not get a lock.
STOW updates a partitioned dataset directory for BPAM files. It adds, changes, replaces, or deletes an entry in the directory. Only one entry can be updated at a time.
Reference Sources
IBM z/OS MVS Diagnosis Reference
IBM z/OS DFSMSdfp Advanced Services
IBM z/OS DFSMS Using Data Sets
IBM z/OS DFSMS Macro Instructions for Data Sets