How to add a device to btrfs without balancing the file system?

Hello,

So I have two drives in my laptop, a 128gb nvme ssd and a 1tb 2.5" ssd. I want to use the fast nvme ssd for the system, but I want to use the 2.5" ssd for Steam games. I have done some searching the web and am left confused. How do i mount the 2.5" ssd as a subvolume on the same filesystem to home/{username}/Games/steam? I do not want to use raid or let the system drive "merge" with the steam drive through rebalancing the file system. When looking it up, would $ btrfs device add /dev/sda /home/{username}/Games/steam make the system files spread over to the steam drive? I mean like the system files from / take space on the Steam drive? I have installed Garuda to the nvme ssd already, I just need to setup steam.

I could be completely wrong. Sorry for the dumb question. Any response is appreciated!

inxi -Faz
System:    Kernel: 5.13.9-zen1-1-zen x86_64 bits: 64 compiler: gcc v: 11.1.0  
parameters: BOOT_IMAGE=/@/boot/vmlinuz-linux-zen root=UUID=c0bcb0ff-64d7-499b-82cd-de923c5e7197  
rw [email protected] quiet splash rd.udev.log_priority=3 vt.global_cursor_default=0
systemd.unified_cgroup_hierarchy=1 resume=UUID=a296e8ec-2bfa-461e-a12b-701ef574ce31 loglevel=3
Desktop: KDE Plasma 5.22.4 tk: Qt 5.15.2 info: latte-dock wm: kwin_x11 vt: 1 dm: SDDM  
Distro: Garuda Linux base: Arch Linux  
Machine:   Type: Laptop System: Dell product: G3 3500 v: N/A serial: <filter> Chassis: type: 10  
serial: <filter>  
Mobo: Dell model: 0X4NG0 v: A00 serial: <filter> UEFI: Dell v: 1.9.0 date: 06/01/2021  
Battery:   ID-1: BAT0 charge: 46.1 Wh (90.4%) condition: 51.0/51.0 Wh (100.0%) volts: 13.1 min: 11.4  
model: SMP DELL PN1VN06 type: Li-poly serial: <filter> status: Charging  
CPU:       Info: Quad Core model: Intel Core i5-10300H bits: 64 type: MT MCP arch: Comet Lake family: 6  
model-id: A5 (165) stepping: 2 microcode: EA cache: L2: 8 MiB  
flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 39999  
Speed: 4251 MHz min/max: 800/4500 MHz Core speeds (MHz): 1: 4251 2: 4240 3: 4282 4: 4282  
5: 4200 6: 4260 7: 4248 8: 4201  
Vulnerabilities: Type: itlb_multihit status: KVM: VMX disabled  
Type: l1tf status: Not affected  
Type: mds status: Not affected  
Type: meltdown status: Not affected  
Type: spec_store_bypass mitigation: Speculative Store Bypass disabled via prctl and seccomp  
Type: spectre_v1 mitigation: usercopy/swapgs barriers and __user pointer sanitization  
Type: spectre_v2 mitigation: Enhanced IBRS, IBPB: conditional, RSB filling  
Type: srbds status: Not affected  
Type: tsx_async_abort status: Not affected  
Graphics:  Device-1: Intel CometLake-H GT2 [UHD Graphics] vendor: Dell driver: i915 v: kernel  
bus-ID: 00:02.0 chip-ID: 8086:9bc4 class-ID: 0300  
Device-2: NVIDIA TU117M [GeForce GTX 1650 Ti Mobile] vendor: Dell driver: nvidia v: 470.57.02  
alternate: nouveau,nvidia_drm bus-ID: 01:00.0 chip-ID: 10de:1f95 class-ID: 0300  
Device-3: Sunplus Innovation Integrated_Webcam_HD type: USB driver: uvcvideo bus-ID: 1-5:4  
chip-ID: 1bcf:2b99 class-ID: 0e02  
Display: x11 server: X.Org 1.20.13 compositor: kwin_x11 driver: loaded: modesetting,nvidia  
display-ID: :0 screens: 1  
Screen-1: 0 s-res: 1920x1080 s-dpi: 96 s-size: 508x285mm (20.0x11.2") s-diag: 582mm (22.9")  
Monitor-1: eDP-1 res: 1920x1080 hz: 120 dpi: 142 size: 344x194mm (13.5x7.6")  
diag: 395mm (15.5")  
OpenGL: renderer: Mesa Intel UHD Graphics (CML GT2) v: 4.6 Mesa 21.1.6 direct render: Yes  
Audio:     Device-1: Intel Comet Lake PCH cAVS vendor: Dell driver: sof-audio-pci-intel-cnl  
alternate: snd_hda_intel,snd_soc_skl,snd_sof_pci_intel_cnl bus-ID: 00:1f.3 chip-ID: 8086:06c8  
class-ID: 0401  
Device-2: NVIDIA vendor: Dell driver: snd_hda_intel v: kernel bus-ID: 01:00.1  
chip-ID: 10de:10fa class-ID: 0403  
Sound Server-1: ALSA v: k5.13.9-zen1-1-zen running: yes  
Sound Server-2: JACK v: 1.9.19 running: no  
Sound Server-3: PulseAudio v: 15.0 running: yes  
Sound Server-4: PipeWire v: 0.3.33 running: no  
Network:   Device-1: Intel Comet Lake PCH CNVi WiFi driver: iwlwifi v: kernel port: 6000 bus-ID: 00:14.3  
chip-ID: 8086:06f0 class-ID: 0280  
IF: wlp0s20f3 state: up mac: <filter>  
Device-2: Realtek RTL8111/8168/8411 PCI Express Gigabit Ethernet vendor: Dell driver: r8169  
v: kernel port: 3000 bus-ID: 04:00.0 chip-ID: 10ec:8168 class-ID: 0200  
IF: enp4s0 state: down mac: <filter>  
IF-ID-1: anbox0 state: down mac: <filter>  
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chip-ID: 8087:0026 class-ID: e001  
Report: bt-adapter ID: hci0 rfk-id: 0 state: up address: <filter>  
Drives:    Local Storage: total: 1.22 TiB used: 20.73 GiB (1.7%)  
SMART Message: Unable to run smartctl. Root privileges required.  
ID-1: /dev/nvme0n1 maj-min: 259:0 vendor: Western Digital model: PC SN530 NVMe WDC 256GB  
size: 238.47 GiB block-size: physical: 512 B logical: 512 B speed: 31.6 Gb/s lanes: 4 type: SSD  
serial: <filter> rev: 21112012 temp: 40.9 C scheme: GPT
ID-2: /dev/sda maj-min: 8:0 vendor: SanDisk model: SDSSDH3 1T02 size: 953.87 GiB block-size:
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ID-3: /dev/sdb maj-min: 8:16 type: USB model: USB DISK 3.0 size: 57.77 GiB block-size:
physical: 512 B logical: 512 B type: N/A serial: <filter> rev: PMAP scheme: MBR
SMART Message: Unknown USB bridge. Flash drive/Unsupported enclosure?
Partition: ID-1: / raw-size: 229.41 GiB size: 229.41 GiB (100.00%) used: 20.73 GiB (9.0%) fs: btrfs
dev: /dev/nvme0n1p2 maj-min: 259:2
ID-2: /boot/efi raw-size: 260 MiB size: 256 MiB (98.46%) used: 562 KiB (0.2%) fs: vfat
dev: /dev/nvme0n1p1 maj-min: 259:1
ID-3: /home raw-size: 229.41 GiB size: 229.41 GiB (100.00%) used: 20.73 GiB (9.0%) fs: btrfs
dev: /dev/nvme0n1p2 maj-min: 259:2
ID-4: /var/log raw-size: 229.41 GiB size: 229.41 GiB (100.00%) used: 20.73 GiB (9.0%) fs: btrfs
dev: /dev/nvme0n1p2 maj-min: 259:2
ID-5: /var/tmp raw-size: 229.41 GiB size: 229.41 GiB (100.00%) used: 20.73 GiB (9.0%) fs: btrfs
dev: /dev/nvme0n1p2 maj-min: 259:2
Swap:      Kernel: swappiness: 133 (default 60) cache-pressure: 100 (default)
ID-1: swap-1 type: partition size: 8.8 GiB used: 0 KiB (0.0%) priority: -2 dev: /dev/nvme0n1p3
maj-min: 259:3
ID-2: swap-2 type: zram size: 7.56 GiB used: 0 KiB (0.0%) priority: 100 dev: /dev/zram0
Sensors:   System Temperatures: cpu: 48.0 C mobo: N/A
Fan Speeds (RPM): N/A
Info:      Processes: 290 Uptime: 4m wakeups: 8 Memory: 7.56 GiB used: 1.79 GiB (23.7%) Init: systemd
v: 249 tool: systemctl Compilers: gcc: 11.1.0 clang: 12.0.1 Packages: pacman: 1678 lib: 505
Shell: fish v: 3.3.1 default: Bash v: 5.1.8 running-in: konsole inxi: 3.3.06
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Your inxi -Faz ?

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In your case, you have drives with different performance characteristics. I wouldn't combine them at the btrfs level, I would combine them at the filesystem level.

In other words, create a btrfs partition on the new drive completely separate from your other btrfs partition. Then create a subvolume for steam. Next add an entry in /etc/fstab to mount the steam subvolume to where you want it to live in your filesystem.

That way your nvme drive and you sata ssd will be separate but still accessible from within the same filesystem.

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