The bootstrap
data set (BSDS)
is a VSAM key-sequenced data set (KSDS). This KSDS contains
information that is critical to DB2®, such as the
names of the logs. DB2 uses
information in the BSDS for system restarts and for any activity that
requires reading the log. 
Specifically, the BSDS contains:
- An inventory
of all active and archive log data sets that are
known to DB2. DB2 uses this information
to track the active and archive log data sets. DB2 also uses this
information to locate log records to satisfy log read requests during
normal DB2 system
activity and during restart and recovery processing.
- A wrap-around
inventory of all recent DB2 checkpoint activity. DB2 uses this information
during restart processing.
- The distributed data facility (DDF)
communication record, which
contains information that is necessary to use DB2 as a distributed
server or requester.
- Information about buffer pools.
Because the BSDS is essential to recovery in the event of subsystem
failure, during installation DB2 automatically
creates two copies of the BSDS and, if space permits, places them
on separate volumes.
The BSDS can be duplexed to ensure availability.