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DSM's TCP Stack Is Limiting Your Remote Access Speed

Mon, 01 Jan 0001 00:00:00 +0000

DSM’s TCP Stack Is Limiting Your Remote Access Speed#

The Problem#

DSM uses CUBIC, Linux’s default TCP congestion algorithm. CUBIC treats dropped packets as a congestion signal and cuts its send rate hard. Packet loss on normal internet connections triggers this constantly, so CUBIC oscillates: brake, ramp up, brake again. The result is a connection sitting at a fraction of what your bandwidth can deliver. This is a kernel-level limitation. No amount of DSM tuning fixes it.

Part 1 - Overview and Architecture

Mon, 01 Jan 0001 00:00:00 +0000

Part 1 - Overview and Architecture#

Before touching any commands, it helps to understand what we are building and why. This page covers the architecture, the problem it solves, and the two-phase approach this guide takes.

What We Are Building#

The goal is an offsite backup destination for Synology Hyper Backup using a Linux server running rsyncd.

Home network                          Offsite location
┌──────────────────┐                 ┌──────────────────────────────┐
│                  │                 │                              │
│  Synology NAS    │── VPN ────────► │  Linux server (rsyncd)       │
│  Hyper Backup    │                 │      │                       │
│                  │                 │      ▼                       │
└──────────────────┘                 │  USB hard drive              │
                                     │  /mnt/backup_hdd             │
                                     │                              │
                                     └──────────────────────────────┘

The Linux machine can be a dedicated server, a repurposed PC, or a virtual machine. It needs storage and network access. That is it.

Part 2 - Drive Setup

Mon, 01 Jan 0001 00:00:00 +0000

Part 2 - Drive Setup#

If you haven’t already, read Part 1 - Overview and Architecture before continuing. This part covers preparing the external hard drive and setting up the folder structure on the Linux server. For Phase 1, this server lives on your LAN.

Environment used in this guide:

Setting	Value
OS	Ubuntu Server
User account	`archive`
Server hostname	`rsync-server`

Prepare the Hard Drive#

Identify the Drive#

Plug in your USB hard drive and confirm it connected at USB 3.0 speed (5000M). If it shows 480M, try a different port.

Part 3 - rsyncd Configuration

Mon, 01 Jan 0001 00:00:00 +0000

Part 3 - rsyncd Configuration#

If you haven’t already, complete Part 2 - Drive Setup before continuing. With storage ready, this part covers installing and configuring rsyncd on the Linux server.

Install rsync#

sudo apt install rsync

Configure rsyncd#

Create the configuration file:

sudo nano /etc/rsyncd.conf

Add the following:

[backup]
path = /mnt/backup_hdd/synology_share
comment = Synology Backup Module
read only = false
timeout = 300
auth users = synology
secrets file = /etc/rsyncd.secrets
uid = archive
gid = archive

Configuration Breakdown#

Setting	Purpose
`[backup]`	Module name. Think of this like a shared folder name (like an SMB share) on a network
`path`	The actual folder on the Linux server where files are stored
`comment`	Description shown when listing modules
`read only`	Set to `false` so files can be written
`timeout`	Kills stuck or frozen sessions after this many seconds
`auth users`	rsync usernames allowed to connect
`secrets file`	Path to the rsync password file
`uid`	User that owns files written through rsync
`gid`	Group that owns files written through rsync

A Note on uid and gid#

rsyncd runs as root and by default writes files as the nobody user. In Part 2 we set specific permissions on the backup directory for the archive account. Setting uid and gid to archive ensures rsync writes files with the correct ownership. Without this you would need to open permissions to “other,” which is not ideal.

Part 4 - Hyper Backup Configuration and Local Seeding

Mon, 01 Jan 0001 00:00:00 +0000

Part 4 - Hyper Backup Configuration and Local Seeding#

If you haven’t already, complete Part 3 - rsyncd Configuration before continuing. With rsyncd running on the LAN, this part covers configuring Hyper Backup and completing the initial seed over gigabit.

Create a New Backup Task#

Open Hyper Backup on your Synology NAS and create a new backup task. When prompted for backup type, select Folders and Packages.

On the next screen, select rsync as the destination type, then select Multiple versions.

Part 5 - Relocating Offsite

Mon, 01 Jan 0001 00:00:00 +0000

Part 5 - Relocating Offsite#

If you haven’t already, complete Part 4 - Hyper Backup Configuration and Local Seeding before continuing. With a full backup on the rsyncd server, this part covers moving the server offsite and routing Hyper Backup through a proxy VM.

What We Are Doing#

There are four pieces of work in this part:

Build a proxy VM on the home network. Enable BBR. Install Tailscale. Configure HAProxy.
Install Tailscale on the rsyncd server.
Physically move the rsyncd server to its offsite location.
Update the Hyper Backup task to point at the proxy VM instead of the rsyncd server directly.

The order matters. Set up Tailscale before you move any hardware. Confirm end-to-end connectivity while everything is still on the LAN. That way if something is wrong you can fix it without driving anywhere.

Understanding VirtualBox Internal Network Adapters

Tue, 11 Nov 2025 00:00:00 +0000

Understanding VirtualBox Internal Network Adapters#

When you create an Internal Network in VirtualBox, three things happen behind the scenes.

VirtualBox creates a virtual switch.
The VM gets a virtual network adapter, just like a real NIC.
A virtual network cable connects the VM’s adapter to the virtual switch.

Think of it like physical computers connecting their network ports to a switch using CAT6 cables.

Creating a Switch#

When you name your Internal Network (for example, “mynetwork”), that name is the switch. Any VM you attach to the same name will land on the same switch. Spelling matters. A typo creates a separate, isolated switch.