send/recv /var single user mode required

[minsonj2016]

Kubuntu 24.04
zfs-2.2.2-0ubuntu9.4
zfs-kmod-2.2.2-0ubuntu9.3

I have been using send/recv with great success .
Then I moved "/var" to a zpool
"ZData1/var-beelink"
This worked without issues
Then I tried to start the incremental backup process using send/recv

zfs snap ZData1/var-beelink@Snap1
zfs send | zfs recv -o mountpoint=/ZBackup7/var-beelink -o canmount=noauto ZBackup7/var-beelink

This works but I notice ZBackup7/var-beelink@Snap1 has a non-zero used amount

Then I
zfs snap ZData1/var-beelink@Snap2
zfs send -i ZData1/var-beelink@Snap1 ZData1/var-beelink@Snap2 | zfs recv -o mountpoint=/ZBackup7/var-beelink -o canmount=noauto ZBackup7/var-beelink

This yields the dreaded "destination volume has changed" error .

The only way I can get this to work is to put the system into single user mode and do the above over

Once that is done and I reboot I can now sync the 2 'vars" without complaint

What am I doing wrong ?

[IvanVolosyuk]

What about setting backup destination to readonly=on ?

[minsonj2016]

OK that worked . I dont quite understand why since the destination volume wasn't modified outside of the send/recv mechanism