Synology NAS sync between offices: the realistic guide

If you have two Synology units in two offices and you want them to stay in sync, you have four reasonable options. They’re each good at different things, and online write-ups tend to confuse them because the names overlap.

This is the version we wish existed when we were figuring it out.

The four options, plainly

Snapshot Replication is Synology’s native cross-NAS replication tool. It works on Btrfs volumes only. It takes Btrfs snapshots on the source and replicates them to a destination NAS. Replication is incremental after the first seed, and you can schedule down to minute-level precision. Good for: fast incremental backup of evolving datasets.

Hyper Backup with Shared Folder Sync is the more general-purpose backup tool. It can go to local disks, USB, cloud, or other NAS. It’s more portable than Snapshot Replication (because it doesn’t require Btrfs at the destination) and supports client-side encryption. Slower for incremental work because it doesn’t ride on snapshots.

Synology Drive ShareSync is real-time, two-way file sync — the closest thing to “Dropbox between two NAS units.” Built for collaboration use cases where both sites want a writable copy of the same folder. Conflict-resolution is built in; latency is higher than Snapshot Replication.

WarpSend Sync (us) is what you reach for when none of the above are fast enough — typically because you’re syncing across the public internet with high RTT and a lot of churn. Same architecture: pick two folders, we keep them in sync. Difference: UDP-based transport with custom congestion control, so the WAN doesn’t bottleneck the sync.

When to use which

Scenario	Recommended
Same building, both NAS on Btrfs, mostly incremental data	Snapshot Replication
Backing up a NAS to a NAS over slow link, want encryption	Hyper Backup
Two sites both editing the same folders	Drive ShareSync
Cross-continent, NAS-to-NAS, high data volume, time-sensitive	WarpSend Sync

If you’re doing #1, stop reading this — Snapshot Replication is great and Synology built it for you.

The thing nobody tells you about the first seed

The first-time sync of any of these is the painful one. If you have 8 TB of shared-folder data and a 100 Mbps upload pipe between offices, theoretical seed time is ~7.4 days of saturated upload — assuming you actually hit line rate the whole time, which you won’t.

Two options to escape that:

1. Ship the seed on a physical drive. Synology specifically supports this for Snapshot Replication — export the initial replication data to external storage on the source side, FedEx the drive to the destination site, import it there. Subsequent replication runs are incremental over the WAN. This is the standard playbook for first-time deployment of any cross-site NAS replication, regardless of tool.

2. Run the seed on WarpSend. UDP transport + parallel streams typically saturates whatever the link can actually carry, so an 8 TB seed on a real-world 100 Mbps link finishes in roughly 1/3 to 1/4 the time of a TCP-based tool — call it 2 days instead of 7+. Still painful, just less.

Whichever you pick, plan for it. The number of Synology cross-site setups that stall at “we’re starting the initial replication” because nobody budgeted a week of wall-clock is legitimately surprising.

The setup gotchas (Snapshot Replication specifically)

If you go with Snapshot Replication, three things will save you a support ticket:

1. Both source and destination must be Btrfs. No exceptions. If your destination NAS has an ext4 volume, you’ll need to reformat before the replication job will accept it.
2. Port 5566 must be open between source and destination — plus DSM’s web UI port. Both sides, both directions. If you’re going across the public internet, this means firewall rules on both end routers.
3. Schedule the snapshot frequency higher than the replication frequency. A replication job only ships snapshots that already exist; if you replicate every 15 minutes but only snapshot every hour, you’re shipping the same snapshot four times.

What WarpSend changes

We built WarpSend Sync because Snapshot Replication is great at what it does (snapshot-aware, Btrfs-native, fast incremental) and bad at what it doesn’t (high-RTT public-internet sync of large, churning datasets). It’s not trying to replace the native Synology stack for local-network use cases. It’s trying to be the answer when you have a NAS in Taipei, a NAS in Berlin, and you need them to stay close to in-sync without buying a leased line.

Install WarpSend from the Synology Package Center, pick two folders, point them at each other. P2P UDP between the two units; Cloudflare relay if NAT punching fails. Real-time sync, resume on disconnect, no router config.

Try it free — 1 TB of monthly traffic, no credit card. If your cross-site sync is currently a multi-day cron job and a hope, this is the upgrade.