Backing up encrypted ZFS datasets you’ll see that ZFS breaks up the encryption hierarchy. The backed up datasets will look like they’ve all been encrypted separately. You can still use the (same) original key to unlock all the datasets, but you’ll have to unlock them separately. 😐
This howto should help you bring them back together when you have to restore from a backup.
Assuming we’ve created a new and encrypted pool to restore the previous backup to (I’ll call it new_rpool). We send our data from the backup pool to new_rpool.
sudo zfs send -w -v backup/laptop/rpool/ROOT@zrepl_20210131_223653_000 | sudo zfs receive -v new_rpool/ROOT
sudo zfs send -w -v backup/laptop/rpool/ROOT/ubuntu@zrepl_20210402_113057_000 | sudo zfs receive -v new_rpool/ROOT/ubuntu
[...]Note that we’re using zfs send -w which sends the encrypted blocks “as is” from the backup pool to new_pool. This means that these datasets can only be decrypted with the key they were originally encrypted with.
Also note that you cannot restore an encrypted root/pool dataset with another encrypted one: i.e. we can’t restore the contents/snapshots of rpool to new_rpool (at least not without decrypting them first on the sender, sending them unencrypted and reencrypting them upon receive). Luckily for me that dataset is empty. 😎
Anyway … our new pool should look something like this now:
$ zfs list -o name,encryption,keystatus,keyformat,keylocation,encryptionroot -t filesystem,volume -r new_rpool
NAME ENCRYPTION KEYSTATUS KEYFORMAT KEYLOCATION ENCROOT
new_rpool aes-256-gcm available passphrase prompt new_rpool
new_rpool/ROOT aes-256-gcm unavailable raw prompt new_rpool/ROOT
new_rpool/ROOT/ubuntu aes-256-gcm unavailable raw prompt new_rpool/ROOT/ubuntu
[...]Note that each dataset is treated as it is encrypted by itself (visible in the encryptionroot property). To restore our ability to unlock all datasets with a single key we’ll have to to some work.
First we have to unlock each of these datasets. We can do this with the zfs load-key command (my data was encrypted using a raw key in a file, hence the -L file:///...):
sudo zfs load-key -L file:///tmp/backup.key new_rpool/ROOT
sudo zfs load-key -L file:///tmp/backup.key new_rpool/ROOT/ubuntu
[...]Although zfs load-key is supposed to have a -r option that works when keylocation=prompt it fails for me with the following error message 🤨:
sudo zfs load-key -r -L file:///tmp/backup.key new_rpool/ROOT
alternate keylocation may only be 'prompt' with -r or -a
usage:
load-key [-rn] [-L <keylocation>] <-a | filesystem|volume>
For the property list, run: zfs set|get
For the delegated permission list, run: zfs allow|unallow
The keystatus should have changed to available now:
$ zfs list -o name,encryption,keystatus,keyformat,keylocation,encryptionroot -t filesystem,volume -r new_rpool
NAME ENCRYPTION KEYSTATUS KEYFORMAT KEYLOCATION ENCROOT
new_rpool aes-256-gcm available passphrase prompt new_rpool
new_rpool/ROOT aes-256-gcm available raw prompt new_rpool/ROOT
new_rpool/ROOT/ubuntu aes-256-gcm available raw prompt new_rpool/ROOT/ubuntu
[...]We can now change the encryption keys and hierarchy by inheriting them (similar to regular dataset properties):
sudo zfs change-key -l -i new_rpool/ROOT
sudo zfs change-key -l -i new_rpool/ROOT/ubuntu
[...]When we list our encryption properties now we can see that all the datasets have the same encryptionroot. This means that unlocking it unlocks all the other datasets as well. 🎉
$ zfs list -o name,encryption,keystatus,keyformat,keylocation,encryptionroot -t filesystem,volume -r new_rpool
NAME ENCRYPTION KEYSTATUS KEYFORMAT KEYLOCATION ENCROOT
new_rpool aes-256-gcm available passphrase prompt new_rpool
new_rpool/ROOT aes-256-gcm available passphrase none new_rpool
new_rpool/ROOT/ubuntu aes-256-gcm available passphrase none new_rpool
[...]Restoring Dataset Properties
This howto doesn’t touch restoring dataset properties, because I’ve not been able to reliably backup dataset properties using the -p and -b options of zfs send. Therefore I make sure that I have a (manual) backup of the dataset properties with something like `zfs get all -s local > zfs_all_local_properties_$(date -Iminutes).txt`