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Limits

Stated plainly, per this series' habit:

  • The password is absolute. Lose every password that opens a key and the repository is ciphertext forever. No check, repair, or support channel changes this; chapter 10.
  • File-level, not image-level. Restic restores files and folders. Rebuilding a dead machine means reinstalling its system and restoring onto it — workable, rehearsed in chapter 8's terms, but not a one-command resurrection.
  • Live databases are not backed up safely by copying their files. The files may be mid-write and mutually inconsistent. Dump, then back up the dump (chapter 12). The same caution applies, more mildly, to any file being actively written during a backup: restic reads what it finds and reports what it could not read.
  • No scheduler, no daemon. Restic runs when something runs it. A laptop that is asleep at 2 a.m. makes no 2 a.m. backup; pick times and tools (cron, systemd timers with wake options, Task Scheduler) that match how the machine actually lives.
  • Deduplication has a memory of its own. Finding chunks in a very large repository takes RAM, roughly in proportion to the repository's size; small machines backing up very large trees can feel it. It is a sizing consideration, not a wall, and it is stated here rather than discovered at 3 a.m.
  • Prune is not free. It re-reads and rewrites data, which on remote and metered backends costs time and money. Retention policies are cheap; sweeping is not. Chapter 9.
  • Metadata has edges. Ownership and permissions restore best as the same user on the same kind of system; Windows and Unix do not mean the same things by them, and the lab's sandbox produced a restore full of ownership warnings with perfect contents (chapter 8). Extended attributes and exotic file types vary by platform and are the first thing to test if they matter to you.
  • One writer at a time, per repository. Locks keep concurrent writers out by design; two machines backing up to one repository take turns or fail on the lock. Schedules should stagger, or repositories should differ.