Begin documenting backup strategy and implementation.

design/BackupStrategy.md

@@ -0,0 +1,17 @@
+Backup Strategy
+
+# Backup Strategy
+## Requirements
+- All data that are difficult or impossible to reconstruct must be backed up and able to be restored from backup if lost.
+- Backups must be automated and must occur without manual interaction with any user.
+- Backups must be monitored and tested on a regular basis, to ensure that
+	1. Backups actually occur when they are scheduled
+	2. Backed-up data can be restored and that the restored data is correct.
+- Backups are encrypted for privacy and security.
+- All data exist in at least three places:  on the device (client or server) where it is used; on a backup device on our home network; and on an off-site device.
+## Strategy
+- On-site backup for client devices will be provided by the Teal server.  The backup tool is Restic, accessible from client devices via SFTP.
+- On-site backup for the Teal server itself will be provided by the Cygnus server (Synology).  Backup is by Restic over SFTP.
+- Off-site backup is not currently implemented.  Two different strategies are being considered:
+	1. Build a custom ZFS-based NAS and deploy it at 28 Carlisle Rd.  This server and the Teal server would provide off-site backup for each other via ZFS send / receive.
+	2. Contract with a cloud storage provider for off-backup, probably either Backblaze using Restic over B2 or rsync.net using ZFS send / receive.