What enqueues are used during Backup of OPEN files?

Document ID : KB000015120
Last Modified Date : 14/02/2018
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Question:

What enqueues are used - or can be used - during Backup of OPEN files?

Answer:

FOR NONVSAM
-----------------
CA Disk needs to get a SHR enque to Backup files and an OLD enqueue for Archive.
If an enqueue can not be obtained, that data set is bypassed and a message is displayed. 

There is a facility that can help capture those enqueued data sets with this Sysparm: 
ARCFDEFR
N (default) - Do not queue request.
Y - Queue a Deferred Archive/Backup request if Archive/Backup failed because the data set was in use.
Then, you can run the Deferred Archive job to try to get the backup or archive.
 
To not do any enqueues during Backups, specify this Sysparm:
USERSENQ with value DMSNOENQ
DMSNOENQ is a module we provide that is used during auto restore.
This is noted in the manual as: Integrity exposure
But, several users use it to get a copy of a data set even if in flight.
Note:  This facility can not be used for Archive processes.
 
If you use USERSENQDMSNOENQ, then you can add this sysparm:
ENQADDTL
N (default) - Do not do an extra enqueue
Y - Will perform an additional enqueue on the QNAME SYSDSN to determine if the
data set is in use.  If so, a message 3715 will be issued stating which data sets
were in use at the time of the backup.
 
FOR VSAM
---------------
This sysparm controls the enqueue level:
VSALOSHR
N (default) - To allocate VSAM defined with SHR(1 3) with DISP=SHR, all others as 'OLD'.
Y - To allocate all VSAM 'DISP=SHR'. (Integrity exposure.)
I admit that in my Storage Admin days, I did use this and felt reasonably safe.
 
If you need to get a "perfect" copy of critical VSAM files that are always in use,
look into the BACKUPCC Command in the Users Guide.