btrfs

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# Btrfs Management

## File System Management

| Command | Description |
|---------|-------------|
| `mkfs.btrfs /dev/sdX` | Create a new Btrfs filesystem |
| `mount /dev/sdX /mnt` | Mount Btrfs filesystem |
| `umount /mnt` | Unmount filesystem |
| `btrfs filesystem show` | Show Btrfs filesystems |
| `btrfs filesystem df /mnt` | Show space usage |
| `btrfs filesystem usage /mnt` | Detailed space usage |

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## RAID Management

| Command | Description |
|---------|-------------|
| `mkfs.btrfs -d raid1 -m raid1 /dev/sdb /dev/sdc` | Create RAID1 (mirror) |
| `mkfs.btrfs -d raid0 -m raid0 /dev/sdb /dev/sdc` | Create RAID0 (striping) |
| `mkfs.btrfs -d raid10 -m raid10 /dev/sdb /dev/sdc /dev/sdd /dev/sde` | Create RAID10 |
| `btrfs device add /dev/sdd /mnt` | Add device to filesystem |
| `btrfs device remove /dev/sdc /mnt` | Remove device from filesystem |
| `btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt` | Convert existing FS to RAID1 |
| `btrfs balance start /mnt` | Rebalance data across devices |
| `btrfs device stats /mnt` | Show device stats |

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## Subvolume Management

| Command | Description |
|---------|-------------|
| `btrfs subvolume create /mnt/data` | Create subvolume |
| `btrfs subvolume list /mnt` | List subvolumes |
| `btrfs subvolume delete /mnt/data` | Delete subvolume |
| `btrfs subvolume snapshot /mnt/data /mnt/data-snap` | Snapshot a subvolume |
| `btrfs subvolume snapshot -r /mnt/data /mnt/data-ro` | Create readonly snapshot |

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## Snapshots

| Command | Description |
|---------|-------------|
| `btrfs subvolume snapshot /mnt/data /mnt/data-snap` | Create snapshot |
| `btrfs subvolume delete /mnt/data-snap` | Delete snapshot |
| `btrfs send /mnt/data-snap | btrfs receive /mnt/backup` | Send snapshot to another FS |

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## Scrub & Check

| Command | Description |
|---------|-------------|
| `btrfs scrub start /mnt` | Start scrub on mounted FS |
| `btrfs scrub status /mnt` | Show scrub status |
| `btrfs scrub cancel /mnt` | Cancel scrub |
| `btrfs check /dev/sdX` | Check filesystem (offline) |
| `btrfs rescue super-recover /dev/sdX` | Try to recover superblock |

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## Resize

| Command | Description |
|---------|-------------|
| `btrfs filesystem resize +10G /mnt` | Grow FS by 10G |
| `btrfs filesystem resize -5G /mnt` | Shrink FS by 5G |
| `btrfs filesystem resize max /mnt` | Use full device size |

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## Example Workflows

### Create RAID1 (mirror) with 2 disks
```bash
mkfs.btrfs -d raid1 -m raid1 /dev/sdb /dev/sdc
mount /dev/sdb /mnt

Add new disk to pool and rebalance into RAID1

btrfs device add /dev/sdd /mnt
btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt

Create snapshot and restore

btrfs subvolume snapshot /mnt/data /mnt/data-snap
btrfs subvolume delete /mnt/data
btrfs subvolume snapshot /mnt/data-snap /mnt/data

---

Qgroups

Command	Description
btrfs qgroup show -re /mnt/btrfs_volume	Shows limits of the volume
btrfs qgroup limit 3T /mnt/btrfs_subvolume	Sets limit for this subvolume

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Mount Options

Option	Description
compress=zstd	Enable compression (recommended: zstd)
compress=lzo	LZO compression (fast, less efficient)
compress-force=zstd	Force compression for all data
autodefrag	Auto defragmentation on write
ssd	Optimize for SSD (usually auto-detected)
ssd_spread	Alternative SSD write strategy
space_cache=v2	Faster mount via allocation cache
discard=async	Asynchronous TRIM for SSD
noatime	Disable access time updates
nodatacow	Disable Copy-on-Write
subvol=	Mount specific subvolume
subvolid=	Mount by subvolume ID

Example fstab entry:

/dev/sdb /mnt btrfs defaults,compress=zstd,autodefrag,ssd,discard=async 0 0