The NAS is now the office's login server. If it dies on Monday at 9 AM, what exactly happens - and what brings the domain back? This is the page to read before that Monday.
Putting the domain on the file NAS concentrates risk in one box. That is manageable - if the backup is real. This page states plainly what a dead DC does to an office (it is less dramatic than feared, and worse than hoped), then lays out the backup routine Synology provides for exactly this job.
First, the calming truth: Windows PCs cache the last successful logins, so staff can usually still sign in to their own PCs and keep working on local files. Now the rest: no new logins on unfamiliar PCs, no password changes, no new users, no Group Policy updates, and - because the DC here is also the file server - the shared folders are down too. The office coasts; it does not function. Every hour of coast spends the goodwill the cache provides, and any PC whose cache is missing (new, rebuilt, or a user who never logged in there) is locked out entirely.
Synology's answer is Hyper Backup: it can back up DSM system configuration and supported packages - including the directory data - to another NAS, an external drive, or cloud storage, on a schedule. Set it to run nightly, keep multiple versions, and store at least one copy off the box (a second device or offsite). Also export the DSM configuration file manually after any big change and keep it with the backup records. A backup that lives only on the same disks as the DC is a copy, not a backup.
Btrfs snapshots and Snapshot Replication are excellent for the shared folders - fast rollback from deletions and ransomware-style damage. But snapshots sit on the same NAS; if the hardware dies, they die with it, and a folder snapshot is not a restore of the domain database. Use snapshots as the quick-undo layer under Hyper Backup, never as its replacement. The 3-2-1 habit applies: three copies, two different media, one offsite.
Keep a written record, stored sealed or in a password manager: the domain name, the NAS name, the domain administrator password, the NAS's static IP, and where the backups live. In a disaster, the person rebuilding may not be the person who built it - and a domain you cannot log into as administrator is a domain you rebuild from zero. This record is also what makes a test restore possible.
Once, before you depend on it: restore the backup to a spare Synology (or a DSM virtual machine), promote the directory, join a test PC in an isolated corner, and log in. Time it. That number - not optimism - is your recovery time, and it decides whether your office also needs the second domain controller covered in this series. Untested backups fail silently at the exact moment they are asked to perform.
The video builds the domain - this page protects it. Watch the build, then set the backup schedule the same day, not next month.
Watch Full VideoUsually yes, on PCs they have used before - Windows caches recent domain logins. But password changes, new users, new PCs and policy updates all stop, and the file shares on that NAS are down. Cached logins are a grace period, not a solution.
Yes - Hyper Backup backs up DSM system configuration and the directory service data for supported packages, and Synology documents domain backup and restore through it. Schedule it, keep versions, and keep a copy off the NAS itself.
No. Snapshots protect against file mistakes and some attacks, but they live on the same hardware. A dead NAS takes its snapshots with it. They are the fast-undo layer; Hyper Backup to another location is the actual domain backup.