When a file is added to the shared folder, the changes start syncing immediately
Resilio Sync needs to detect file changes / updates before it starts the procedure of file indexing and delivery. Resilio Sync uses following techniques of file changes detection:
Filesystem Notifications
The fastest way for Sync to detect changes inside the synchronized folder. When FS notifications work properly, Sync starts processing file immediately after the update. Although FS notifications have a number of limitations and for some file storages the system notifications are not even supposed to work. For example, NFS or SMB2 mounted shares, a deeply nested folder on a Windows PC, etc.
Scheduled folder scan
By default it runs every 600 seconds (10 minutes) and on Sync start. This is a reliable mechanism to discover file updates for cases when file system notifications don't work.
To make this rescan as lightweight as possible, Sync only checks for file and folder modification time and size changes. If anything has changed, it rehashes the whole file to find out which pieces of files have actually changed and need to be synced.
It is possible to change the period of automatic rescanning of sync folders. You can do it in "Preferences > Advanced > Power user preferences", see folder_rescan_interval setting.
If set to zero, Sync won't rescan folders at all, even upon restart. You might need it in the following cases:
- really many files on your storage, so folder rescan time is comparable to the rescan period.
- file changes are rare or never happen.
- Sync prevents your storage drive from entering power saving mode.
On-demand folder rescan
Can be manually triggered at any time with "Rescan" button in share's preferences.