Import existing zfs pool.md

Import existing ZFS pool

There might be times you will want to import an existing ZFS pool. For example, after an OS reinstallation. This is how to do it.

Steps

1. After logging in, assume root by running sudo -i.
2. Create the keys directory: mkdir /keys. It is assumed that this address is the same one used before reinstalling the OS and that the pool will look for the key in the same directory. Adjust the address if not.
3. Copy the key from another computer: scp user@host:/path/to/keyfile /keys/Tank.dat. Change {user@host:/path/to/keyfile} to the address of the key on the computer containing the backup. If you prefer, you can also use a USB stick to transfer the key backup.
4. Import the existing pools: zpool import -d /dev/disk/by-id -a. If the pool was not exported before, try using -f to force the import.
5. Mount all datasets and load the key if necessary: zfs mount -al.
6. Restore the container folders from the hard drives to the SSD: rsync -avz /mnt/Tank/Apps/ /Apps/.
7. Run: ./scripts/generate_dataset_mount_units.sh. This will generate Systemd units that will mount the datasets in Tank automatically after loading the key upon rebooting the server. Run this command cat /etc/zfs/zfs-list.cache/Tank to verify that the cache file is not empty. If it is empty, try running the script again as it means the cache and units were not generated.

Note

After import, there will be certain steps in the guide that you can skip. For example if certain directories or files already existed. It is left to the reader's discretion to see which steps are no longer necessary.

Tip

To adjust the max size of ZFS ARC use the command echo {size_in_bytes} > /sys/module/zfs/parameters/zfs_arc_max replacing {size_in_bytes} with the size in bytes you wish to set. To make the change permanent execute the command echo "options zfs zfs_arc_max={size_in_bytes}" > /etc/modprobe.d/zfs.conf && dracut --force.

Caution

Assigning a very high value can cause instability in the system, only change it if you know what you are doing.