Syncthing vs Nextcloud

Start here, because it is the part people learn the expensive way: Syncthing is not a backup and it is not a server.

Not a backup, because every change propagates. The official FAQ states it plainly. Delete a folder on your laptop and it is gone from the NAS within seconds, exactly as designed. Encrypt your documents with ransomware and the encrypted versions replicate to every device before you have finished reading the ransom note.

Not a server, because there is no server. Every device is an equal peer holding a full copy of each folder it shares. There is no central instance to point clients at, no admin console over the fleet, no accounts, and no way to give someone read-only access to one folder without giving them a full replica of it.

Nextcloud is the opposite of both statements. It is authoritative, it has a database, a trash bin, file versions, quotas, per-user permissions and share links you can send to someone who has never heard of it. It costs correspondingly more to run.

What the spec table is telling you#

Operational load, 1 against 4, is the headline and it is honest in both directions. Syncthing has no database service, no reverse proxy requirement, no certificate you provision and a config that is one XML file. Nextcloud has three major upgrades a year that you cannot skip.

Services to run says 1 for Syncthing, but read it as one per device: three laptops and a NAS is four installations, four config directories and four device keys. Idle memory at 60 MB against 600 MB is real, with the caveat that Syncthing's memory scales with the number of files tracked rather than their size, so a million tiny files costs more than a few large ones. Stack planner holds the figures if you are budgeting a box.

Which one lets you send somebody a link#

Nextcloud, and this is usually the deciding requirement rather than anything about sync quality.

Nextcloud gives you user accounts, groups, quotas, per-folder shares, public links with passwords and expiry, WebDAV, mobile apps, and a web UI that a person who is not you can operate. It also gives you the rest of the suite: calendar, contacts, collaborative documents. If the requirement includes anyone outside your own device fleet, Syncthing simply does not do the job, and no amount of configuration makes it.

Syncthing gives you folders that are identical across machines you control. Sharing means adding another device ID as a peer, which hands over a full copy and full write access unless you set that peer's folder to receive-only. That is a fine model for your own laptop and a terrible one for your accountant.

Which one destroys your files faster#

Both can. Only one does it at line speed.

Syncthing's dangerous defaults are worth spelling out:

• Deletions propagate immediately. The mitigation is a receive-only folder on the archival device, so the NAS accepts changes but never sends its own, and a destructive change on a laptop leaves the server copy marked out of sync rather than deleted.
• Conflicts create files, they do not merge. Two devices editing between syncs produces filename.sync-conflict-<date>-<time>-<deviceid>.ext. Nothing warns you, and the copies replicate everywhere.
• File versioning is off until you configure it. Turn on staggered or simple versioning per folder with a real retention policy, and remember .stversions/ grows and is not pruned unless you say so.
• Tombstones expire after six months. Since 2.0, deleted-file records are dropped after six months (--db-delete-retention-interval). A device that has been offline longer and then rejoins can resurrect files the cluster deleted, as new files.

Nextcloud's trash and version history give you a real undo, per user, with retention policy. That is a genuine safety feature and it is the reason a household with non-technical users is usually better served by it.

What running each one actually looks like#

Syncthing is one binary or one container per device, and that is the entire architecture:

services:
  syncthing:
    image: syncthing/syncthing:latest
    hostname: nas
    network_mode: host          # needed for local discovery on 21027/udp
    volumes:
      - ./config:/var/syncthing/config
      - /srv/shared:/var/syncthing/shared

It serves the GUI on 127.0.0.1:8384, syncs on 22000 TCP and UDP, and discovers peers on 21027 UDP. Pair devices by exchanging IDs and accepting on both ends. Nothing has to exist first: no database, no certificate you provision, no DNS. Since 2.0 it does not even create a default ~/Sync folder.

Nextcloud is four containers with a real database, Redis for file locking, a reverse proxy and a five-minute cron. Set up Redis before you have users, use system cron rather than AJAX for background jobs, and choose Postgres or MariaDB at install time. SQLite is offered by the installer, survives a single-user trial, and then collapses under concurrent sync clients with locking errors.

The backup shapes differ just as sharply. Syncthing: your synced folders are ordinary files, back them up with whatever you already use, and keep config.xml and the device key pair, because losing them changes your device ID and forces you to re-pair every peer. Nextcloud: occ maintenance:mode --on, then config/, the data directory and a database dump taken together, or the dump and the files will disagree about which uploads exist.

What happens on upgrade day#

Syncthing 2.0 (12 August 2025) replaced LevelDB with SQLite. The index migrates on first launch, one way, and on large setups it is a wait rather than a blip: plan downtime on the device with the biggest folders and do not interrupt it. That release also stopped publishing prebuilt binaries for several platforms, including DragonFly BSD, illumos, Solaris, linux/ppc64, NetBSD and windows/arm, so check your architecture before upgrading. Otherwise Syncthing upgrades are unremarkable, which is why it scores 1 on operational load.

Nextcloud ships majors about every four months with twelve-month support and no skipping: reach the latest point release of your current major, step to the next major's latest, repeat. Each step is gated on PHP compatibility and on every installed app being ready. That is two or three windows a year, forever, and it is the honest price of the features in the previous section. An update strategy that does not lose data is how you keep it boring.

Using both, correctly#

The combination that works is Syncthing for your own devices and Nextcloud for people, with one rule: do not let Syncthing write into Nextcloud's data directory.

Nextcloud's database is the index of that directory. Files that appear underneath it are invisible until occ files:scan runs, ownership is easy to get wrong, and you will eventually hit a state where the database and the disk disagree. The supported shape is to sync into a separate path and mount that path into Nextcloud as a local External Storage, which is designed for content another process manages.

The other useful pairing is Syncthing as the transport and a real backup tool as the safety net: phone camera roll to a receive-only folder on the server, then restic snapshots of that folder to somewhere neither device can reach. If photos are the actual workload, Immich does the job properly and Immich vs Nextcloud for photos covers where that line sits.

The verdict, by situation#

What to do next#

If you picked Syncthing, do three things before you trust it. Set the server-side folder to receive-only. Enable staggered file versioning with a retention policy you actually chose. Then run a real backup tool against that folder on a schedule (restic vs BorgBackup picks one), so that the copy of last resort lives somewhere Syncthing cannot reach. Test the restore once. Leave the GUI on localhost and reach it over a tunnel (Remote access without port forwarding).

If you picked Nextcloud, the first hour is Redis, system cron and a real database, and the first month is deciding who is responsible for the upgrade windows. Put it behind a proper reverse proxy (Reverse proxy and TLS) and take the backup with maintenance mode on, not from a running instance.

If you are replacing a commercial service, Replace Dropbox walks the full migration. The rest of the category is in Photos and files.