ZFS

I've just installed Devuan Excalibur using mostly the OpenZFS instructions for Debian Trixie, as I did before except with Chimaera (which I then upgraded to Daedalus.) I had a grand old time getting it to boot and started over a couple of times, which is not a big deal because it does not take very long to get to the point where it doesn't boot. I had been using legacy booting and chose to try UEFI, which is working okay now.

I run Devuan Linux, because I don't like systemd and I do like Debian. I have root on ZFS, which is a great way to protect your data but also comes with challenges. I wanted to install Linux 6.14 because I want NTSYNC support, but the latest release of OpenZFS for Linux does not support Kernel 6.14. However, the master branch of ZFS does support it, and has for a while now, so I decided to build ZFS myself so that I could upgrade my kernel.

Without getting [too] technical (and probably operating "above my pay grade") the ZFS ZIL is a place where synchronous writes are done, and you can move this to a separate zpool, which is called a SLOG. One SLOG can store the ZIL for multiple zpools. While most writes by most applications are asynchronous, some are not, and file metadata writes are synchronous. Putting the ZIL for a HDD (or even an array) on a SSD lets your zpool provide the IOPS performance of your SLOG, while also avoiding fragmentation and reducing seeks through ordered writes.

I have recently made the switch as a Linux user from LUKS, LVM and ext4 to ZFS, ZFS, and ZFS. I started it with Ubuntu, which conveniently offered me an encrypted root on zfs option which worked very well for me in general. However, every time I had to interface with systemd it felt like a chore, when what I really wanted was the old school UNIX feel I got from Slackware. And now I've converted to Devuan 4 "Chimaera" on ZFS, which is based on Debian 11 "Bullseye", which is as close to that as I'm willing to get given the amount of work I want to do. In the process, I've had to mount my old zfs filesystems on my new system gracefully, and this is how I went about that.

This is based on a number of documents, beginning with OpenZFS Debian Bullseye Root on ZFS. There are some notable changes. View the original document and follow along:

One of my favorite features of modern filesystems is the sparse file, where "empty" portions of files are unallocated, so they don't consume any space. This allows oversubscription of disk blocks, so long as you never actually complete fill all of the files at once. But one common problem of sparse files is that they tend to grow, and there is often no way to solve this problem in place. But there is, with ZFS.