What the bootstrap data set is for

BSDS (bootstrap data set), dual mode" /> What the bootstrap data set is for

What the bootstrap data set is for

The bootstrap data set (BSDS) is a VSAM key-sequenced data set (KSDS) that holds information needed by WebSphere MQ. It contains the following:

An inventory of all active and archived log data sets known to WebSphere MQ. WebSphere MQ uses this inventory to:

Track the active and archived log data sets
Locate log records so that it can satisfy log read requests during normal processing
Locate log records so that it can handle restart processing
WebSphere MQ stores information in the inventory each time an archive log data set is defined or an active log data set is reused. For active logs, the inventory shows which are full and which are available for reuse. The inventory holds the relative byte address (RBA) of each portion of the log held in that data set.
A wrap-around inventory of all recent WebSphere MQ activity. This is needed if you have to restart the queue manager.

The BSDS is required if the queue manager has an error and you have to restart it. WebSphere MQ must have a BSDS. To minimize the likelihood of problems during a restart, we can configure WebSphere MQ with dual BSDSs, each recording the same information. This is known as running in dual mode. If possible, the copies should be on separate volumes. This reduces the risk of them both being lost if the volume is corrupted or destroyed. You should use dual BSDSs rather than dual write to DASD.
The BSDS is set up when WebSphere MQ is customized and we can manage the inventory using the change log inventory utility (CSQJU003). This utility is discussed in the WebSphere MQ for z/OS System Administration Guide. It is referenced by a DD statement in the queue manager startup procedure.
Normally, WebSphere MQ keeps duplicate copies of the BSDS. If an I/O error occurs, it deallocates the failing copy and continues with a single BSDS. We can restore dual mode operation, this is described in the WebSphere MQ for z/OS System Administration Guide.
The active logs are first registered in the BSDS when WebSphere MQ is installed. We cannot replace the active logs without terminating and restarting the queue manager.
Archive log data sets are allocated dynamically. When one is allocated, the data set name is registered in the BSDS. The list of archive log data sets expands as archives are added, and wraps when a user-determined number of entries has been reached. The maximum number of entries is 1000 for single archive logging and 2000 for dual logging.
We can use a tape management system to delete the archive log data sets (WebSphere MQ does not have an automated method). Therefore, the information about an archive log data set can be in the BSDS long after the archive log data set has been deleted by the system administrator.
Conversely, the maximum number of archive log data sets could have been exceeded, and the data from the BSDS dropped long before the data set has reached its expiry date.
We can use the following MQSC command to determine the extent of the log, and the name of the active or archive log data set holding the earliest log RBA, required for various types of media or queue manager recovery:
DISPLAY USAGE TYPE(DATASET)
If the system parameter module specifies that archive log data sets are cataloged when allocated, the BSDS points to the integrated catalog facility (ICF) catalog for the information needed for later allocations. Otherwise, the BSDS entries for each volume register the volume serial number and unit information that is needed for later allocations.