Backup-while-open data sets (IMS)

DFSMSdss supports backup-while-open processing of IMS™ data sets by providing for fast replication copies and concurrent copy dumps. IMS requests backup through the application programming interface of DFSMSdss, described in Application programming interface.

Backup-while-open serialization is applicable to HISAM, SHISAM, and index (primary and secondary) databases.

Backup as an open data set for IMS is triggered through a UIM request, rather than through a backup-while-open status or BWO(TYPEIMS) definition as CICS® does.

Specifics of IMS backup-while-open support are outlined in Table 1.

Note: During a logical data set dump, you must specify VALIDATE (directly or by default) to ensure that an IMS backup-while-open data set that is dumped while updates are being made can be successfully restored. VALIDATE allows DFSMSdss to validate and correct the data set during the dump process, or to end the dump (with an ADR943E message) if the data set is in an unrecoverable state.

DFSMSdss issues an ADR943E message during logical data set dump if the NOVALIDATE parameter is used with an indexed VSAM data set defined as BWO(TYPEIMS).

Table 1. DFSMSdss Support for IMS Backup-While-Open Data Sets
Topic:	For IMS data sets:
Can non-VSAM data sets be copied or dumped as open data sets?	Yes
Can non-indexed VSAM data sets be copied or dumped as open data sets?	Yes
Must indexed VSAM data sets be specifically designated as being BWO-eligible to be copied or dumped as open data sets?	No
How are indexed VSAM data sets designated as being eligible for update activity detection through a BWO counter?	By defining the data set as BWO(TYPEIMS)
How is backup as an open data set triggered?	Through a UIM request
How is bypassing of enqueues on SYSDSN and SYSVSAM managed?	Automatically

Attention: The user must be aware that COPY with DELETE, DUMP with DELETE, and RESTORE with REPLACE can cause irreparable damage to an IMS data set for the following reasons:

The enqueue serialization obtained by COPY and DUMP are insufficient to ensure that the data set is not also being used by an IMS application in an environment where GRS (or equivalent) is not being used.
COPY and DUMP do not provide any special handling for any data set defined as BWO(TYPEIMS).
RESTORE does not provide any protection against reallocating or overwriting any IMS data set for which RESTORE is able to obtain an enqueue serialization on SYSDSN and SYSVSAM.