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Hobbyist

Filesystem requirements

works everywhere, cheaply on some

Hobbyist runs on any filesystem. On a reflink-capable one, copying a project is nearly free. On the rest it is a real copy, which is correct and slow and costs full disk space.

Which is which

Section titled “Which is which”
Filesystem Reflinks Notes
XFS with reflink=1 yes The default on modern mkfs.xfs. The usual recommendation on Linux
ZFS yes Also gives you snapshots of its own
APFS yes macOS. Nothing to configure
Btrfs yes
ext4 no The default image on a lot of cheap VPS providers

Check what you have:

Terminal window
df -T ~/.hobby            # Linux
mount | grep " / "        # macOS

hobby init also reports it, and warns rather than failing when reflinks are absent.

What needs them

Section titled “What needs them”
Feature Without reflinks
Snapshots A full copy: slow, and full disk cost. Also not reachable yet
Copy-on-write branching, Phase 1.5 The same. Not built yet
Everything else Unaffected

Day to day, running databases and apps and workers, this makes no difference at all. It matters when you copy a project.

The ext4 problem, stated plainly

Section titled “The ext4 problem, stated plainly”

ext4 is the default root filesystem on a lot of the cheap VPS providers this project is aimed at, and it has no reflink support at any version. This is not something a configuration flag fixes.

If cheap copies matter to you and you are provisioning a new box, choose XFS at install time, or attach a second volume formatted XFS or ZFS and point $HOBBY_HOME at it:

Terminal window
export HOBBY_HOME=/mnt/fast/hobby

That is the supported way to keep state on a different disk, and it is the one change that turns a cheap VPS into a machine where copies are free.

Postgres 18, and why the floor is lower than it looks

Section titled “Postgres 18, and why the floor is lower than it looks”

Cloning a stopped data directory is version independent. Cloning one that is awake needs Postgres 18 or newer.

Because everything here hibernates, most instances are stopped most of the time, so the version requirement applies far less often than it first appears. That claim was worth checking rather than assuming, and the research is filed at docs/branching/research/2026-08-07-cloning-a-stopped-data-directory.md.