Time Machine Backups

While sharing, the device advertises itself as a Time Machine destination, so a Mac on the same network can back up to the drawer device. No configuration on the server side, and a timely replacement as AFP-based targets go away.

Setting up the Mac

Open System Settings → General → Time Machine and click Add Backup Disk…
Pick the "Time Machine" share on "NAS Reborn (device name)" from the list of available disks.
Sign in with a device account when asked.

The backup folder is created on the server automatically the first time the Mac connects. From then on it behaves like any Time Machine disk: hourly backups while the Mac is on the network, and restore through the normal Time Machine browser or during migration to a new Mac.

Space to grow

A Mac's backup history is usually larger than an old phone's internal storage, so for more than a token backup, put the destination on a USB drive. When a Mac first sets up Time Machine, the app offers to move the new backup folder onto a drive; the same move is available any time from the folder's own screen, and it keeps the share name and addresses, so the Mac keeps backing up to the same destination. See External Drives for adapters, power and formats. Every private folder the server shares appears in the Mac's destination picker, so a folder added straight from a drive works too.

Backups are never squeezed by the free tier: storage limits apply to web and S3 serving only, and files arriving over SMB, Time Machine included, are never blocked. The backup folder does not count against the free tier's folder limit either, since it is created for you the first time a Mac backs up and a free feature should not become a surprise paywall. Time Machine manages its own space within the disk, thinning old backups as the disk fills.

A backup is never a web page. A folder holding a Time Machine backup is a complete copy of somebody's Mac, so the server refuses every anonymous web request for it whatever its access level says, and offers no switch to change that. Your Mac, signed-in browsers and signed S3 clients reach it exactly as before.

Keeping backups reliable

A Time Machine backup is a long, stateful operation, and a target that disappears mid-write is worse than one that was never there. Two habits keep the target trustworthy:

Keep NAS Reborn in front on the server device. Sharing pauses whenever the app leaves the screen, so use Guided Access or Single App Mode as described in Always-On Serving.
Keep the device plugged in, so a backup never dies to an empty battery.

A network Time Machine target on a spare phone is a fine everyday backup, and the watchdog tells you if it ever stops serving. For data you cannot afford to lose, follow the classic advice of more than one backup in more than one place.