Solved Replication Question about -F switch

[Peacekeeper2000]

It is more a understanding question : the man zfs says under zfs send -R

... If the -F flag is specified when this stream is received, snapshots and file systems that do not exist on the sending side are destroyed.

As a non-native speaker I have difficulties to understand, what is destroyed: the snap shot and filesystem on the sending side or on the receiving side ?
As a practical example: I have two zfs filesystems ( send/source & recv/target ) and 6 snapshots named a-f in the following setup

send/source@a
	recv/target@b
send/source@c	recv/target@c
send/source@d
send/source@e
send/source@f

I do a kind of zfs send -R -I @a send/source@f | zfs recv -F recv/target What will be the result ? Will recv/target@b be deleted or all snapshots on send/source that are not existing on recv/target ?

 

[zirias@]

This flag is used on the receiving side and will only destroy things on the receiving side that were already destroyed on the sending side. It makes a lot of sense in backup scripts

edit: to further reassure you: zfs send is a read-only operation, only zfs recv will ever write something, and it will only write to the target you give it. A pipe is unidirectional (from the sender to the receiver), so there is no way for a zfs recv to modify anything you send, it can't even know its source.

 

[Alain De Vos]

The f from force.

 

[Peacekeeper2000]

ok, so zfs recv will do an analytics of the received data.It will then identify snapshots that are available on recv/target but have not received from the stream. These identified snapshots will be destroyed on recv/target. In case of the example, it will destroy recv/target@b
So it will clean up the backup from historical data, but is also dangerous if you want to keep the history. It also will not over-write the recv/target@c - I assume the above example will fail with a destination has snapshots error.

I think I need to change my strategy how to name the snapshots. Currently the snapshot names are the weekday names. In a roll-over the snapshot ist converted to a bookmark. The two weeks old bookmarks are deleted. I had hope that the -F switch allows a sort of consolidation on both sides.