btrfs-modules-4.7.0-1-s390x-di software package provides BTRFS filesystem support, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install btrfs-modules-4.7.0-1-s390x-di
btrfs-modules-4.7.0-1-s390x-di is installed in your system.
Make ensure the btrfs-modules-4.7.0-1-s390x-di package were installed using the commands given below,
$ sudo dpkg-query -l | grep btrfs-modules-4.7.0-1-s390x-di*
You will get with btrfs-modules-4.7.0-1-s390x-di package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | debian-installer udeb packages |
| Package | btrfs-modules-4.7.0-1-s390x-di |
| Version | 4.7.8-1 |
| Description | BTRFS filesystem support |
| Sub Section | Debian-installer |