Backup Bandwidth Throttling and Scheduling

Why Throttle Backups?

Backups can consume significant bandwidth and I/O, especially initial full backups. Without throttling, they can saturate your network, increase user latency, and cause disk I/O contention. Proper throttling ensures backups complete without degrading service quality.

Network Bandwidth Throttling

# Rsync with bandwidth limit
rsync -avz --bwlimit=50000 /var/www/ backup-server:/backup/www/

# Dynamic throttling based on time of day
HOUR=$(date +%H)
if [ "$HOUR" -ge 8 ] && [ "$HOUR" -lt 22 ]; then
    BWLIMIT="--bwlimit=10000"   # 10 MB/s business hours
else
    BWLIMIT="--bwlimit=0"       # Unlimited at night
fi
rsync -avz $BWLIMIT /data/ backup:/backup/data/

# Rclone time-based schedule
rclone sync /backup remote:bucket --bwlimit "08:00,10M 23:00,100M 00:00,off"

# Restic bandwidth limits
restic backup /data --limit-upload 20480  # 20 MB/s

I/O Throttling

# Lowest I/O and CPU priority
ionice -c 3 nice -n 19 /usr/local/bin/backup.sh

# Systemd service with resource limits
[Service]
Type=oneshot
ExecStart=/usr/local/bin/backup.sh
Nice=19
IOSchedulingClass=idle
CPUWeight=10
IOWeight=10
MemoryMax=4G

Intelligent Scheduling

#!/bin/bash
# Smart backup - defer if server is busy
LOAD=$(awk '{print $1}' /proc/loadavg)
THRESHOLD=$(echo "$(nproc) * 0.7" | bc)

if (( $(echo "$LOAD > $THRESHOLD" | bc -l) )); then
    echo "Load too high, deferring..."
    echo "/usr/local/bin/smart-backup.sh" | at now + 30 minutes
    exit 0
fi

# Check network utilization
RX1=$(cat /sys/class/net/eth0/statistics/rx_bytes)
sleep 2
RX2=$(cat /sys/class/net/eth0/statistics/rx_bytes)
BW_MBPS=$(( (RX2 - RX1) / 2 / 1024 / 1024 * 8 ))

if [ "$BW_MBPS" -gt 800 ]; then
    echo "Network busy, deferring..."
    echo "/usr/local/bin/smart-backup.sh" | at now + 15 minutes
    exit 0
fi

ionice -c 3 nice -n 19 restic backup /data --limit-upload 10240

Monitoring Performance

START=$(date +%s)
START_BYTES=$(cat /sys/class/net/eth0/statistics/tx_bytes)

restic backup /data --limit-upload 20480

DURATION=$(($(date +%s) - START))
TRANSFERRED=$(( ($(cat /sys/class/net/eth0/statistics/tx_bytes) - START_BYTES) / 1048576 ))
echo "Backup: ${TRANSFERRED}MB in ${DURATION}s" >> /var/log/backup-perf.log

Best Practices

• Schedule full backups off-peak; incremental backups can run during day with throttling
• Use ionice class 3 (idle) so backups never compete with production I/O
• Monitor completion times for trends
• Use time-based throttling profiles that adjust automatically
• Always leave bandwidth headroom
• Verify throttled backups still complete within your backup window