Problems using USB drive sneakernet to seed incremental replication

[alugowski]

My home FreeNAS, let's call it Sender, has a handful of datasets that I'd like to replicate off-site to another FreeNAS, let's call it Receiver. I already had a Replication Task that would copy those datasets to a pool named usb_backup that lives on an external USB drive. My home upload speed is terrible, and I'm traveling to the remote location anyway, I thought I'd export and travel with usb_backup and use that as a seed for a new incremental backup.

I arrived, and copied the datasets to Receiver using zfs send usb_backup/foo | zfs receive tank/foo.

I then went to set up a new Replication Task on Receiver that will pull that same dataset from Sender. When I did so I got this message:

Destination dataset does not contain any snapshots that can be used as a basis for the incremental changes in the snapshots being sent. The snapshots in the destination dataset will be deleted and the replication will begin with a complete initial copy.

I read that it's possible to do what I'm trying to do, so what did I do wrong? Is it possible to salvage my replication seed? A full transfer will take two weeks, I'd like to avoid that.

 

[sretalla]

copied the datasets to Receiver using zfs send usb_backup/foo | zfs receive tank/foo.

That's not the normal way to zfs send | recv ... you need to send a snapshot, not the dataset. Check the source dataset (usb_backup) for snapshots and do the send again with the last one available. That may make it possible to continue replication.

 

[alugowski]

Thank you @sratella. You're right, I was sending a snapshot. The problem is that I had created a new migrate snapshot and zfs sent that.

I instead deleted the migrate snapshot, found the latest auto-generated snapshot, and used:

Code:

zfs send usb_backup/foo@auto-2020-06-14_00-00 | pv | zfs receive -F tank/foo

and then the Replication Task succeeded quickly as expected. I think my mental model of how snapshots work is missing something. I thought I can use any snapshot as a base, but apparently it matters how the snapshot was created. Thanks for your help!