# 创建只读快照
sudo btrfs subvolume snapshot -r /mnt/@data /mnt/@snapshots/data-full

# 全量发送到另一个 Btrfs 文件系统
sudo btrfs send /mnt/@snapshots/data-full | sudo btrfs receive /backup/

# 发送到文件
sudo btrfs send -f /backup/data-full.send /mnt/@snapshots/data-full

# 创建新的只读快照
sudo btrfs subvolume snapshot -r /mnt/@data /mnt/@snapshots/data-incr

# 增量发送（-p 指定父快照）
sudo btrfs send -p /mnt/@snapshots/data-full /mnt/@snapshots/data-incr | \
    sudo btrfs receive /backup/

# 增量发送到文件
sudo btrfs send -p /mnt/@snapshots/data-full /mnt/@snapshots/data-incr \
    -f /backup/data-incr.send

# 快照链：snap1 → snap2 → snap3 → snap4
# 可以基于任何相邻快照做增量

# snap1 → snap2（增量基于 snap1）
sudo btrfs send -p /snap1 /snap2 | sudo btrfs receive /backup/

# snap2 → snap3（增量基于 snap2）
sudo btrfs send -p /snap2 /snap3 | sudo btrfs receive /backup/

# snap1 → snap4（大增量，但可以）
sudo btrfs send -p /snap1 /snap4 | sudo btrfs receive /backup/

# 全量发送到远程服务器
sudo btrfs send /mnt/@snapshots/data-full | \
    ssh user@backup-server "sudo btrfs receive /backup/"

# 增量发送到远程服务器
sudo btrfs send -p /mnt/@snapshots/data-old /mnt/@snapshots/data-new | \
    ssh user@backup-server "sudo btrfs receive /backup/"

# 带进度监控
sudo btrfs send /mnt/@snapshots/data-full | \
    pv | ssh user@backup-server "sudo btrfs receive /backup/"

# 使用压缩数据传输（节省带宽）
sudo btrfs send --compressed-data /mnt/@snapshots/data-full | \
    ssh user@backup-server "sudo btrfs receive /backup/"

# 接收端（备份服务器）
nc -l -p 9999 | sudo btrfs receive /backup/

# 发送端（生产服务器）
sudo btrfs send /mnt/@snapshots/data-full | nc backup-server 9999

#!/bin/bash
# btrfs-backup.sh - Btrfs 自动化增量备份脚本
set -euo pipefail

# 配置
SOURCE_MNT="/mnt/data"
BACKUP_HOST="backup-server"
BACKUP_USER="backup"
BACKUP_PATH="/backup/data"
SNAPSHOT_DIR="/mnt/@snapshots"
SUBVOLUMES=("@home" "@var" "@config")
KEEP_SNAPSHOTS=10
LOG_FILE="/var/log/btrfs-backup.log"

# 日志函数
log() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*" | tee -a "$LOG_FILE"
}

# 获取最新快照
get_latest_snapshot() {
    local subvol="$1"
    sudo btrfs subvolume list -s "$SOURCE_MNT" | \
        grep "path ${SNAPSHOT_DIR##*/}/${subvol}-" | \
        sort -t'-' -k2 | tail -1 | awk '{print $NF}'
}

# 创建只读快照
create_snapshot() {
    local subvol="$1"
    local timestamp=$(date '+%Y%m%d-%H%M%S')
    local snap_name="${subvol}-${timestamp}"
    local snap_path="${SNAPSHOT_DIR}/${snap_name}"

    log "Creating snapshot: $snap_name"
    if sudo btrfs subvolume snapshot -r "${SOURCE_MNT}/${subvol}" "$snap_path" 2>>"$LOG_FILE"; then
        echo "$snap_name"
    else
        log "ERROR: Failed to create snapshot $snap_name"
        return 1
    fi
}

# 发送增量备份
send_backup() {
    local subvol="$1"
    local new_snap="$2"
    local parent_snap="$3"

    if [[ -n "$parent_snap" ]]; then
        log "Sending incremental: $parent_snap → $new_snap"
        sudo btrfs send -p "${SNAPSHOT_DIR}/${parent_snap}" "${SNAPSHOT_DIR}/${new_snap}" | \
            ssh "${BACKUP_USER}@${BACKUP_HOST}" "sudo btrfs receive ${BACKUP_PATH}/" 2>>"$LOG_FILE"
    else
        log "Sending full: $new_snap"
        sudo btrfs send "${SNAPSHOT_DIR}/${new_snap}" | \
            ssh "${BACKUP_USER}@${BACKUP_HOST}" "sudo btrfs receive ${BACKUP_PATH}/" 2>>"$LOG_FILE"
    fi
}

# 清理旧快照
cleanup_snapshots() {
    local subvol="$1"
    local snapshots=($(sudo btrfs subvolume list -s "$SOURCE_MNT" | \
        grep "path ${SNAPSHOT_DIR##*/}/${subvol}-" | \
        sort -t'-' -k2 | awk '{print $NF}'))

    local count=${#snapshots[@]}
    if (( count > KEEP_SNAPSHOTS )); then
        local to_delete=$(( count - KEEP_SNAPSHOTS ))
        log "Cleaning up $to_delete old snapshots for $subvol"
        for (( i=0; i<to_delete; i++ )); do
            local snap="${snapshots[$i]}"
            log "Deleting: $snap"
            sudo btrfs subvolume delete "${SOURCE_MNT}/${snap}" 2>>"$LOG_FILE" || true
        done
    fi
}

# 主流程
main() {
    log "=== Starting Btrfs backup ==="

    for subvol in "${SUBVOLUMES[@]}"; do
        log "--- Processing $subvol ---"

        # 获取最新的本地快照
        local latest=$(get_latest_snapshot "$subvol")

        # 创建新快照
        local new_snap=$(create_snapshot "$subvol")

        # 发送备份
        send_backup "$subvol" "$new_snap" "$latest"

        # 清理旧快照
        cleanup_snapshots "$subvol"
    done

    log "=== Backup completed ==="
}

main "$@"

# /etc/systemd/system/btrfs-backup.timer
[Unit]
Description=Btrfs Backup Timer

[Timer]
OnCalendar=*-*-* 02:00:00
Persistent=true
RandomizedDelaySec=600

[Install]
WantedBy=timers.target

# /etc/systemd/system/btrfs-backup.service
[Unit]
Description=Btrfs Backup Service
After=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/btrfs-backup.sh
User=root

# 启用定时备份
sudo systemctl enable --now btrfs-backup.timer

# 1. 检查备份服务器上的快照
ssh backup-server "sudo btrfs subvolume list /backup"

# 2. 比较源和目标的文件数量
SOURCE_COUNT=$(sudo find /mnt/@data -type f | wc -l)
BACKUP_COUNT=$(ssh backup-server "sudo find /backup/@data -type f | wc -l")
echo "Source: $SOURCE_COUNT files, Backup: $BACKUP_COUNT files"

# 3. 校验关键文件的哈希
sudo sha256sum /mnt/@data/important.db
ssh backup-server "sudo sha256sum /backup/@data/important.db"

# 从备份恢复（在备份服务器上）
sudo btrfs subvolume snapshot /backup/@data /restore/data-restored

# 验证恢复的数据
sudo diff -r /backup/@data /restore/data-restored