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# Splitting `~/hdd` (sda3) to grow the root btrfs pool
> **Superseded as the primary fix.** A later investigation found the actual
> largest reclaimable consumer on the pool is `/var/home/ironmagma` itself
> (11G), not something that needs more pool capacity to fix — see
> [`relocate-home-to-hdd.md`](./relocate-home-to-hdd.md), which frees that
> space directly instead of growing the pool to make room for it. This doc
> is kept for reference / as a fallback if more headroom is still wanted
> later.
## TL;DR
The root filesystem is a bootc/Fedora Atomic (uBlue Aurora) install where `/`,
`/home`, and `/var` are separate **btrfs subvolumes on the same physical
partition** (`nvme0n1p3`, 23.5 GiB total). That pool is at ~89% full with only
~1.7 GiB free, which caused a Discord crash (SIGBUS while writing its disk
cache — see [Trigger](#trigger)). `/var` itself only holds ~169 MiB, so the
actual space pressure lives elsewhere in the shared pool (likely `/home` or
ostree deployment data), not in `/var` specifically — **that root cause
should still be identified and possibly cleaned up for free before doing any
of this**, since this plan doesn't fix the cause, it just gives the pool more
room.
The plan: shrink the ext4 partition on the secondary HDD (`sda3`, mounted at
`~/hdd`) to free ~100 GiB at the end of the disk, create a new partition
(`sda4`) in that space, then add `sda4` as a second device to the nvme btrfs
pool (`btrfs device add` + `btrfs balance`).
**Not yet executed** — this doc captures the plan and exact numbers as of
the date below, for when this project picks it back up.
## Hardware / software identification
- Distro: Aurora (uBlue/Fedora Atomic, bootc-based), KDE Plasma
- Kernel: `7.1.8-200.fc44.x86_64`
- Root filesystem layout (`/etc/fstab`):
```
UUID=8d071437-8c47-4669-94a5-4a669a3b3b66 / btrfs subvol=root,compress=zstd:1,ro
UUID=8d071437-8c47-4669-94a5-4a669a3b3b66 /home btrfs subvol=home,compress=zstd:1
UUID=8d071437-8c47-4669-94a5-4a669a3b3b66 /var btrfs subvol=var,compress=zstd:1
UUID=a45a95fa-805f-43f2-bc32-8da8970c1b91 /var/home/ironmagma/hdd ext4 defaults,nofail
/var/home/ironmagma/hdd/flatpak /var/lib/flatpak none bind,nofail
```
`/`, `/home`, and `/var` are three subvolumes of **one** btrfs partition
(`nvme0n1p3`), so they share a single free-space pool.
- `nvme0n1p3` (the OS btrfs pool): 23.5 GiB total, 20.9 GiB used, 1.7 GiB
free (89% full) at time of writing.
- `sda` (secondary HDD, GPT): `sda1` EFI System, `sda2` Apple APFS (leftover
from a prior macOS install — unused, not touched by this plan), `sda3`
Microsoft basic data (ext4), which is the **last** partition on the disk.
- `sda3` (`~/hdd`, ext4): 456.9 GiB total, 174.5 GiB used, 259.2 GiB free
(41% full) at time of writing. Already bind-mounted at `/var/lib/flatpak`
in fstab, so all flatpak app data already lives here.
## Trigger
```
Sep 26 01:12:11 imac audit[11852]: ANOM_ABEND ... comm="CacheThread_Blo" ... sig=7 res=1
Sep 26 01:12:11 imac systemd-coredump[20186]: Process 11852 (Discord) ... terminated abnormally with signal 7/BUS, processing...
Sep 26 01:12:12 imac systemd-coredump[20187]: Cannot store coredump of 11852 (Discord): No space left on device
```
Discord (Flatpak) crashed with SIGBUS on a Chromium cache thread — classic
symptom of a memory-mapped cache file hitting a full filesystem — and the
subsequent coredump couldn't even be written, confirming the pool was
nearly out of space.
## Why not just relocate `/var` wholesale
Considered and rejected: bind-mounting all of `/var` (not just
`/var/lib/flatpak`) onto the HDD, the same way flatpak already is.
- `/var`'s own subvolume is only ~169 MiB — moving it wouldn't free
meaningful space, since the 89%-full number is pool-wide, not `/var`-only.
- `/var` holds state systemd needs very early in boot (NetworkManager
profiles, container/podman storage, machine state). The existing
`/var/lib/flatpak` bind mount is `nofail` and only needed well after boot;
making all of `/var` depend on an external/secondary disk being ready in
time is a much larger risk — a slow-to-init or disconnected HDD could
leave the system unable to start normal services, not just unable to
launch flatpak apps.
Growing the existing btrfs pool (this doc's plan) avoids that: the pool
gains capacity, but nothing critical becomes dependent on the HDD being
present at early boot in a way it isn't already.
## Plan
### 0. Prerequisites
- Back up anything on `sda3` you can't afford to lose. This is a resize of
an in-use partition holding 174.5 GiB of real data (including all flatpak
app data), not a no-risk operation.
- `sudo` needs an interactive password/TTY in this environment — these
steps must be run from a real terminal, not automated non-interactively.
- `/var/lib/flatpak` (on `sda3`) is held open by far more than just Discord
— confirmed via `fuser -vm /var/lib/flatpak`: Chrome, 1Password, Dolphin,
Konsole, KWrite, `xdg-desktop-portal`, and Plasmashell all had handles
into it. A live unmount from inside the desktop session isn't realistic;
do this from a plain TTY (Ctrl+Alt+F3) after logging out of the
graphical session, not from a terminal window inside it.
### 1. Shrink `sda3` (ext4) to free ~100 GiB at the end
From a TTY, logged out of the graphical session:
```bash
sudo umount /var/lib/flatpak
sudo umount /var/home/ironmagma/hdd
# required before any resize — stop here if this reports errors
sudo e2fsck -f /dev/sda3
# shrink filesystem well below the future partition size for safety margin
# (current usage 174.5 GiB; new partition will be ~356.9 GiB)
sudo resize2fs /dev/sda3 350G
# shrink the partition to match, using parted's "from the end" syntax —
# sda3 is the last partition on the disk, so this leaves clean trailing
# free space
sudo parted /dev/sda resizepart 3 -100GiB
```
### 2. Create `sda4` in the freed space
```bash
sudo parted /dev/sda unit GiB print
# note sda3's new End value, then:
sudo parted /dev/sda mkpart primary <sda3-new-End> 100%
```
### 3. Verify before doing anything else
```bash
sudo mount /var/home/ironmagma/hdd
sudo mount /var/lib/flatpak
lsblk -f
```
Reboot once, log back into the normal graphical session, and confirm
flatpak apps (Discord included) still launch fine before proceeding to
step 4. Don't chain step 4 onto the same session — verify this part is
solid first.
### 4. Add `sda4` to the nvme btrfs pool
Not yet detailed to exact commands — high-level:
```bash
sudo btrfs device add /dev/sda4 /
sudo btrfs balance start /
```
Open questions to resolve before running this step:
- Balance filters, if any, to control how data gets distributed rather than
spread arbitrarily across both devices.
- Whether to convert to a specific btrfs profile (e.g. keep `single` data
profile across both devices, vs. something with redundancy) — plain
`single` means losing `sda4` (or the whole `sda` disk) can take out data
that landed there, including parts of `/`, `/home`, or `/var`. This
raises the HDD from "flatpak-only dependency" to "part of the core OS
pool" — a real increase in blast radius that should be a deliberate
choice, not a default.
## Open risks / unknowns
- Exact root cause of the pool being 89% full was never identified in the
session that produced this doc — only ruled out `/var` itself (169 MiB).
Should check `rpm-ostree status` / `bootc status` for stale deployments
and `du` on `/home` before assuming this resize is even necessary; some
or all of the space may be reclaimable for free.
- `sda2` (Apple APFS, unused leftover from a prior macOS install on this
disk) was not investigated as an alternative space source — reclaiming it
instead of shrinking `sda3` was not evaluated.
- Once `sda4` joins the btrfs pool, disk health/failure handling for `sda`
matters a lot more than it does today. Not yet decided whether to monitor
it differently once it's part of the OS pool.
---
*Written 2026-09-26, based on a live investigation of a Discord crash caused
by the pool being full. No resize has been performed yet.*

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# Relocating `/var/home/ironmagma` onto the HDD (sda3)
## TL;DR
The nvme btrfs pool (`/`, `/home`, `/var` subvolumes sharing one ~23.5 GiB
partition) is ~92% full and caused a Discord SIGBUS crash (full disk cache
write — see [`hdd-partition-split-for-btrfs-pool.md`](./hdd-partition-split-for-btrfs-pool.md)
for that investigation). Breakdown of the ~20.9 GiB used:
| Location | Size |
|---|---|
| `/sysroot/ostree/repo` (the OS image itself, one deployment, not staged) | 8.4G |
| `/var/home/ironmagma` (actual `$HOME` — lives in the "home" subvolume) | 11G |
| `/var` itself (logs/cache) | 169M |
`/var/home/ironmagma` is the single biggest reclaimable chunk and is not
part of the OS image, so relocating it onto the HDD (`sda3`, mounted at
`~/hdd`, 259G free at time of writing) fixes the actual problem directly,
rather than just giving the pool more room to keep filling up
(the partition-split doc's approach).
**Not yet executed.** This must be run from a TTY after a full logout —
Claude Code itself runs from files under `$HOME`, so it cannot perform or
supervise this live; there is no assistant available mid-procedure. Follow
this doc standalone.
## Why this is trickier than the existing flatpak bind mount
`/var/lib/flatpak` is already bind-mounted from the HDD
(`/var/home/ironmagma/hdd/flatpak`), which works because the *bind mount's
source* is nested a level below where the HDD itself is mounted, and none of
that nesting is itself the target of another mount.
Relocating `$HOME` is different: the HDD (`sda3`) is currently mounted
**inside** the very directory (`/var/home/ironmagma`) we want to replace
with a bind mount. If we tried to keep that nesting and just bind-mount some
subdirectory of the HDD back onto `/var/home/ironmagma`, the new mount would
sit *on top of* the path leading to the HDD mount itself — Linux mount
shadowing means the original `sda3` mount (and the flatpak bind nested
inside it) would become unreachable via the normal path afterward, even
though it's technically still mounted underneath. **This is why the HDD's
mount point must first move to a path that is a sibling of `/var/home/ironmagma`,
not a descendant of it** (e.g. `/var/hdd` instead of
`/var/home/ironmagma/hdd`).
## Pre-flight checks done (safe, no changes made)
- Grepped for hardcoded references to the old `/var/home/ironmagma/hdd`
path across `~/Code` and `~/.config`: no scripts, systemd units, or build
configs depend on it. Only two trivial, non-blocking references found:
- `~/.config/spectaclerc` — Spectacle's screenshot save folder
- `~/.config/session/dolphin_dolphin_dolphin` — a remembered Dolphin tab
Both just need re-pointing after the move; neither blocks anything.
- Current relevant `/etc/fstab` lines:
```
UUID=a45a95fa-805f-43f2-bc32-8da8970c1b91 /var/home/ironmagma/hdd ext4 defaults,nofail 0 2
/var/home/ironmagma/hdd/flatpak /var/lib/flatpak none bind,nofail 0 0
```
## Plan
### Phase 0 — from the normal desktop session, before logging out
1. **Take a real backup of `/var/home/ironmagma`** to somewhere independent
of this machine's disks (external drive, another machine, cloud). The
copy made in Phase 2 is *not* a substitute for this — it lands on the
same physical HDD this plan is otherwise trusting; a real backup is the
actual safety net if something goes wrong mid-procedure.
2. Note down anything you'd hate to lose track of that isn't obviously
under `$HOME` in the usual places (e.g. GPG/SSH agent state, browser
session you care about) so you can sanity-check it post-move.
### Phase 1 — drop to a TTY
Log out of the graphical session fully (this ends the current Claude Code
session too). Switch to a TTY (Ctrl+Alt+F3) and log in as `ironmagma`.
### Phase 2 — move the HDD's mount point out from under `$HOME`
```bash
sudo mkdir -p /var/hdd
sudo umount /var/lib/flatpak
sudo umount /var/home/ironmagma/hdd
```
Edit `/etc/fstab`, changing:
```
UUID=a45a95fa-805f-43f2-bc32-8da8970c1b91 /var/home/ironmagma/hdd ext4 defaults,nofail 0 2
/var/home/ironmagma/hdd/flatpak /var/lib/flatpak none bind,nofail 0 0
```
to:
```
UUID=a45a95fa-805f-43f2-bc32-8da8970c1b91 /var/hdd ext4 defaults,nofail 0 2
/var/hdd/flatpak /var/lib/flatpak none bind,nofail 0 0
```
Then:
```bash
sudo systemctl daemon-reload
sudo mount /var/hdd
sudo mount /var/lib/flatpak
ls /var/hdd # sanity check: should show the same old contents, incl. flatpak/
```
Home directory content is untouched by this phase — `/var/home/ironmagma`
still has its old (now unused) empty `hdd/` placeholder directory in it,
harmless, cleaned up later.
### Phase 3 — copy `$HOME` onto the HDD
Nothing is mounted inside `/var/home/ironmagma` anymore at this point, so
this is a plain, non-nested copy:
```bash
sudo rsync -aHAX --info=progress2 /var/home/ironmagma/ /var/hdd/home-ironmagma/
```
`-aHAX` preserves permissions, hardlinks, ACLs, and xattrs (including
SELinux labels stored as `security.selinux` xattrs — matters for `.ssh`
permissions and SELinux contexts).
### Phase 4 — verify before touching the original
```bash
sudo diff -rq /var/home/ironmagma /var/hdd/home-ironmagma
```
Should report no differences. Do not proceed if it does.
### Phase 5 — swap
```bash
sudo mv /var/home/ironmagma /var/home/ironmagma.old
sudo mkdir /var/home/ironmagma
sudo chown ironmagma:ironmagma /var/home/ironmagma
```
Add to `/etc/fstab`:
```
/var/hdd/home-ironmagma /var/home/ironmagma none bind 0 0
```
**Deliberately no `nofail` here**, unlike the hdd/flatpak lines. If the HDD
fails to come up, we want boot to visibly stop and demand attention, not
silently hand you a freshly-empty `/var/home/ironmagma` that looks like your
whole home directory vanished.
```bash
sudo systemctl daemon-reload
sudo mount /var/home/ironmagma
ls -la /var/home/ironmagma # should show all the familiar dotfiles/dirs
sudo restorecon -R /var/home/ironmagma # SELinux label safety net
```
### Phase 6 — test before rebooting
```bash
sudo -u ironmagma touch /var/home/ironmagma/.relocate-test
ls -la /var/home/ironmagma/.relocate-test
rm /var/home/ironmagma/.relocate-test
```
### Phase 7 — reboot and verify for real
Reboot, log into the normal graphical session, and check:
- SSH agent / keys work
- `git` works in `~/Code`
- Dropbox resumes syncing
- 1Password unlocks
- Browser profile intact
- Claude Code itself starts (it lives under `$HOME` — if this doc is
readable again from inside a working Claude Code session, that's a good
sign the move succeeded)
- Re-point Spectacle's save folder and check the stale Dolphin tab (see
pre-flight checks above)
### Phase 8 — only once fully confident (a few days of normal use)
**Nothing before this step actually frees space on the nvme pool** — until
now we've only relocated and kept a full fallback copy. This is the step
that does it:
```bash
sudo rm -rf /var/home/ironmagma.old
```
This drops nvme pool usage from ~92% to roughly ~43%.
### Optional cleanup
- `/var/home/ironmagma/hdd` no longer exists as a mountpoint (it's `/var/hdd`
now); if you want a convenience path at the old location, a plain symlink
works fine since nothing is mounted there anymore:
```bash
ln -s /var/hdd /var/home/ironmagma/hdd
```
## Open risks / unknowns
- Whether SELinux contexts translate perfectly onto ext4 via rsync `-X` —
`restorecon -R` in Phase 5 is the safety net, but not independently
verified here.
- Making the home bind mount required (no `nofail`) means a failed/missing
HDD blocks login entirely rather than degrading gracefully. This is a
deliberate choice (see Phase 5) but worth revisiting if the HDD turns out
to be less reliable than expected.
- The still-unexplained podman `system df` discrepancy (reports 2.412GB of
"reclaimable" images with an empty image list, real 2.3G sitting in
`~/.local/share/containers/storage/overlay`, and 9 volumes that return
`Permission denied` on inspection) was not resolved — separate from this
plan, and worth checking whether those volumes belong to a still-used
distrobox/toolbox environment before ever running `podman system reset`.
---
*Written 2026-09-26. No steps executed yet.*