ZFS incremental send on recursive snapshot

[frenziedengi]

I am trying to understand ZFS send behavior, when sending incrementally, for the purposes of backup to another (local) drive.

Consider the following situation:

• volume = tank
• Datasets: tank/stuff1, tank/stuff2
• I take a recursive snapshot:
  Code:

  zfs snapshot -r tank@initial

• I send it:
  Code:

  zfs send -R tank@initial | zfs recv -Fduv tankb/tank

• Later on, I create a new data set: tank/stuff3
• I take a recursive snapshot:
  Code:

  zfs snapshot -r tank@second

• I send it, incrementally:
  Code:

  zfs send -Ri @initial tank@second | zfs recv -Fduv tankb/tank

Question:What happens to tank/stuff3, since it was not present in the initial snapshot set sent over?
Follow up: How do people typically handle this situation where you would like to keep things incremental, but datasets may be created at a later time?

I investigated what happens some. I get this error when doing this second send:

Code:

local fs tank/stuff3 does not have fromsnap (initial in stream); must have been deleted locally; ignoring

Ultimately, it appears that the contents of stuff3 are transferred as part of this exchange. How does this work? What does "ignoring" mean?

 

[Dusan]

It's ignoring the incremental option and creating a full stream for that dataset. A comment from libzfs_sendrecv.c:

Code:

        /*
        * If this fs does not have fromsnap, and we're doing
        * recursive, we need to send a full stream from the
        * beginning (or an incremental from the origin if this
        * is a clone).  If we're doing non-recursive, then let
        * them get the error.
        */

If you try to do a non recursive replication while missing the initial snapshot you will get a hard error -- the replication will fail. If you do a recursive replication you will see the warning, but the replication will proceed sending a full stream.

 

[frenziedengi]

Excellent. This is exactly the behavior I wanted.
Thanks for the research to the source!