As we have talked about the concepts of crash consistent and application consistent backup, when it comes to the backup of production system, these concepts also exists.
Using external storage, the mechanism of production backup on a backup system is based on Flashcopy. How to do Flashcopy? There are some ways, and these ways determined the type of final backup.
Some possible ways to do backup is power off system, end subsystems, quiesce and warm flash. By powering off system, or end subsystems, for Flashcopy, we get an image level copy of production data on backup system. In this kind of backup, there is no memory data lost, no pending transactions, no corrupted data, etc. By using quiesce, usually, application I/O operations are held, and incomplete transactions will be completed, then a Flashcopy is done. In this way, an application consistent copy is made for backup system. If we don’t like powering off system, ending subsystems, and even quiesce, then we use warm flash. Warm flash means no matter what is being done on the production system, just do a Flashcopy, so memory data is lost, pending transitions are not completed, so you see, this is a crash consistent copy for backup system.
Which one is best? There is no one answer for all. You have to make a decision based on what you need and what you can bear.