Tor Relay on ARM Hardware: Raspberry Pi and ARM Servers in 2026

Modern ARM processors include the ARM Cryptography Extensions (ARMv8-A CE) for hardware-accelerated AES and SHA operations, equivalent to Intel's AES-NI. Support by hardware: Raspberry Pi 4 (Cortex-A72): supports ARMv8 Cryptography Extensions, AES acceleration available. Raspberry Pi 5 (Cortex-A76): same, with higher single-core performance. ARM Cortex-A53 (many embedded boards): ARMv8 but Cryptography Extensions are optional - check specific chip. Ampere Altra (cloud ARM server): full ARMv8.2-A with Cryptography Extensions. AWS Graviton 3: Neoverse V1, full crypto acceleration. Verify crypto acceleration is available: openssl speed -evp aes-256-ctr should show 1-5 Gbit/s throughput on modern ARM; old ARM without CE shows 50-200 Mbit/s. The 10-20x difference makes CE essential for relay performance.

Raspberry Pi 4 (1-8GB RAM) and Pi 5 can run productive Tor relays for low to moderate bandwidth. Expected performance: Pi 4 at 100 Mbit/s relay: CPU utilization 40-70%, stable operation. Pi 4 at 200 Mbit/s: borderline, occasional CPU saturation. Pi 5 at 200-300 Mbit/s: feasible with proper OS configuration. Network connection matters more than CPU for Pi relays: Pi 4/5 have Gigabit Ethernet but most home internet connections are slower. A Pi relay on a 100 Mbit/s home connection: set BandwidthRate 80 MBits. OS: use Raspberry Pi OS 64-bit (aarch64) for maximum performance - 32-bit OS cannot use ARMv8 Crypto Extensions. Tor package: apt install tor on Raspberry Pi OS installs the Debian package. Ensure it is a recent version (Tor 0.4.8+); older versions may not use CE by default.

ARM VPS providers for Tor relay operation: Hetzner Cloud - offers ARM instances (CAX series) at competitive prices, good for Tor relay operation. Oracle Cloud Free Tier - provides ARM instances (Ampere A1) with 4 OCPUs and 24GB RAM free, excellent for relay operation. AWS Graviton3 (a-series instances) - highest performance ARM, suitable for high-bandwidth relays. Scaleway STARDUST1 (ARM) - very affordable ARM instances. Expected throughput on ARM VPS: Oracle A1 (4 OCPUs Ampere Altra) handles 1-2 Gbit/s Tor relay traffic; Hetzner CAX11 (2 vCPUs, equivalent to Cortex-A78 approximately) handles 200-500 Mbit/s. ARM VPS often provides better performance-per-dollar than x86 VPS for Tor relay workloads.

Package managers often provide slightly outdated Tor versions. For latest features and ARM-specific optimizations, compile from source: Install dependencies: apt install build-essential autoconf automake libtool libssl-dev libevent-dev zlib1g-dev. Download source: get from torproject.org/download/tor/. Configure with crypto flags: ./configure --enable-gcc-hardening CFLAGS='-O2 -march=native'. The -march=native flag enables ARM-specific optimizations including Cryptography Extension instructions for AES and SHA. Build: make -j$(nproc) (parallel build using all cores). Install: make install. Verify build: tor --version shows the version and linked libraries. Test AES acceleration: run openssl speed -evp aes-256-ctr after building to confirm software is using hardware acceleration.

Single-board computers (Raspberry Pi) generate significant heat when running Tor relays at high utilization. Uncooled Pi 4/5 throttles CPU speed when temperature exceeds 80C. At throttled speed, relay throughput drops 30-50%. Passive cooling: heat sink case (Argon ONE, FLIRC) keeps Pi 4 below 70C at moderate load without a fan. Active cooling: small 5V fan reduces temperatures significantly. Required for sustained 200+ Mbit/s operation on Pi 4/5. Monitor temperature: vcgencmd measure_temp for Raspberry Pi. thermal_zone in /sys/class/thermal/ for generic ARM boards. Configure thermal throttling threshold: raspi-config -> Performance Options -> Overclock or thermal management settings. Run a stress test (stress --cpu 4) while monitoring temperature to determine if additional cooling is needed before deploying as a relay.