My linux config and rc files https://git.sommerfeld.dev/dotfiles/atom/etc/systemd/system/btrfs-balance@.service?h=master 2026-05-13T12:43:35Z 2026-05-13T12:43:35Z sommerfeld sommerfeld@sommerfeld.dev 2026-05-13T12:43:35Z urn:sha1:14a6992a4ebe826266a1ea4320c34c0ac91932ee Template service+timer that runs `btrfs balance start -dusage=50 -musage=50 %f` once a month on the instance's mount path. Mirrors the shape of the stock btrfs-scrub@.{service,timer} so the operational model is identical: enable btrfs-balance@-.timer for /, btrfs-balance@\ x2dhome.timer for /home, etc. Why a partial balance and not a full one: full `btrfs balance start` rewrites every block group, which on a multi-TB volume takes hours and can chew through enormous amounts of CSUM/free-space-tree work. `-dusage=50 -musage=50` only consolidates block groups that are less than half full, which is exactly the operation that reclaims space 'lost' to fragmentation after lots of small writes — the only practical reason a healthy single-disk btrfs needs balancing at all. `Nice=19 IOSchedulingClass=idle` keeps it out of the way of foreground work; `KillSignal=SIGINT` (same as btrfs-scrub) lets a graceful Ctrl-C checkpoint the operation cleanly. Persistent=true catches the run on next boot if the machine was off when the timer fired. Enabled in systemd-units/system.txt as btrfs-balance@-.timer (root volume only — /home isn't a separate subvolume on this machine).