On a FreeBSD 11.1 system, I created a zpool that contains all my jails that are created and managed with py3-iocage (built from ports) 0.99.1. I have set up my system to have zfs snapshots of the pool created and then backed up to an external hard drive connected via USB using zfs send/receive. Here is my process: Create snapshot: zfs snapshot -r iocage@`date +"%Y-%m-%d_%H:%M:%S"` Initial backup: zfs send -R iocage@date1 | zfs receive -vF backups/iocage backups is the zpool on my external HDD, which is imported at an altroot Incremental backup: zfs send -R -i iocage@date1 iocage@date2 | zfs receive -vF backups/iocage The problem: Before I sent my initial backup to my external HDD I ran this command: zfs send -R iocage@date1 | zfs receive -vnF backups/iocage This, however, produced this error: root@homeServer:~ # zfs send -R iocage@2017-08-19 | zfs receive -vnF backups/iocage would receive full stream of iocage@2017-08-19 into backups/iocage@2017-08-19 would receive full stream of iocage/iocage@2017-08-19 into backups/iocage/iocage@2017-08-19 would receive full stream of iocage/iocage/download@2017-08-19 into backups/iocage/iocage/download@2017-08-19 would receive full stream of iocage/iocage/download/11.1-RELEASE@2017-08-19 into backups/iocage/iocage/download/11.1-RELEASE@2017-08-19 would receive full stream of iocage/iocage/download/10.3-RELEASE@2017-08-19 into backups/iocage/iocage/download/10.3-RELEASE@2017-08-19 would receive full stream of iocage/iocage/releases@2017-08-19 into backups/iocage/iocage/releases@2017-08-19 would receive full stream of iocage/iocage/releases/10.3-RELEASE@2017-08-19 into backups/iocage/iocage/releases/10.3-RELEASE@2017-08-19 would receive full stream of iocage/iocage/releases/10.3-RELEASE/root@2017-08-19 into backups/iocage/iocage/releases/10.3-RELEASE/root@2017-08-19 would receive full stream of iocage/iocage/releases/11.1-RELEASE@2017-08-19 into backups/iocage/iocage/releases/11.1-RELEASE@2017-08-19 would receive full stream of iocage/iocage/releases/11.1-RELEASE/root@nextcloud into backups/iocage/iocage/releases/11.1-RELEASE/root@nextcloud cannot receive incremental stream: destination 'backups/iocage/iocage/releases/11.1-RELEASE/root' does not exist warning: cannot send 'iocage/iocage/releases/11.1-RELEASE/root@minecraft': signal received warning: cannot send 'iocage/iocage/releases/11.1-RELEASE/root@webServer': Broken pipe warning: cannot send 'iocage/iocage/releases/11.1-RELEASE/root@plexMedia': Broken pipe warning: cannot send 'iocage/iocage/releases/11.1-RELEASE/root@homeBackup': Broken pipe warning: cannot send 'iocage/iocage/releases/11.1-RELEASE/root@reverseProxy': Broken pipe warning: cannot send 'iocage/iocage/releases/11.1-RELEASE/root@2017-08-19': Broken pipe I saw that it was saying backups/iocage/iocage/releases/11.1-RELEASE/root didn't exist, so I created that path, with each directory being its own zfs dataset (like it is on host). Once I did that, I got a new error: zfs send -R iocage/iocage@2017-08-19 | zfs receive -vnF backups/iocage would receive full stream of iocage/iocage@2017-08-19 into backups/iocage@2017-08-19 would receive full stream of iocage/iocage/download@2017-08-19 into backups/iocage/download@2017-08-19 would receive full stream of iocage/iocage/download/11.1-RELEASE@2017-08-19 into backups/iocage/download/11.1-RELEASE@2017-08-19 would receive full stream of iocage/iocage/download/10.3-RELEASE@2017-08-19 into backups/iocage/download/10.3-RELEASE@2017-08-19 would receive full stream of iocage/iocage/releases@2017-08-19 into backups/iocage/releases@2017-08-19 would receive full stream of iocage/iocage/releases/10.3-RELEASE@2017-08-19 into backups/iocage/releases/10.3-RELEASE@2017-08-19 would receive full stream of iocage/iocage/releases/10.3-RELEASE/root@2017-08-19 into backups/iocage/releases/10.3-RELEASE/root@2017-08-19 would receive full stream of iocage/iocage/releases/11.1-RELEASE@2017-08-19 into backups/iocage/releases/11.1-RELEASE@2017-08-19 would receive full stream of iocage/iocage/releases/11.1-RELEASE/root@nextcloud into backups/iocage/releases/11.1-RELEASE/root@nextcloud would receive incremental stream of iocage/iocage/releases/11.1-RELEASE/root@minecraft into backups/iocage/releases/11.1-RELEASE/root@minecraft would receive incremental stream of iocage/iocage/releases/11.1-RELEASE/root@webServer into backups/iocage/releases/11.1-RELEASE/root@webServer would receive incremental stream of iocage/iocage/releases/11.1-RELEASE/root@plexMedia into backups/iocage/releases/11.1-RELEASE/root@plexMedia would receive incremental stream of iocage/iocage/releases/11.1-RELEASE/root@homeBackup into backups/iocage/releases/11.1-RELEASE/root@homeBackup would receive incremental stream of iocage/iocage/releases/11.1-RELEASE/root@reverseProxy into backups/iocage/releases/11.1-RELEASE/root@reverseProxy would receive incremental stream of iocage/iocage/releases/11.1-RELEASE/root@2017-08-19 into backups/iocage/releases/11.1-RELEASE/root@2017-08-19 would receive full stream of iocage/iocage/templates@2017-08-19 into backups/iocage/templates@2017-08-19 would receive full stream of iocage/iocage/jails@2017-08-19 into backups/iocage/jails@2017-08-19 would receive full stream of iocage/iocage/jails/webServer@2017-08-19 into backups/iocage/jails/webServer@2017-08-19 cannot receive: local origin for clone backups/iocage/jails/webServer/root@2017-08-19 does not exist warning: cannot send 'iocage/iocage/jails/webServer/root@2017-08-19': signal received However, as I said, removing -n from my input, the error goes away and the send/receive is successful.
I am not sure that zfs can simulate reception of replications streams sufficiently well. It lacks the machinery to simulate creation of new datasets which might be required to simulate reception of subordinate datasets. But it does detect when a dataset that is supposed to be received already exists. I am not sure if it is worth the trouble perfecting the dry mode.