Backup and restore (#12)

* Create backup_and_restore.md

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* Update backup_and_restore.md

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---------

Co-authored-by: Jiaqiang Xu <xjqkilling@gmail.com>

manual/usage/backup_and_restore.md

@@ -0,0 +1,65 @@
+## Overview
+
+There are generally two parts of data to backup
+- SeaSearch index metadata
+- SeaSearch index document data
+
+The index metadata is saved in a local BoltDB file by default. The document data for the indexes is saved either to local storage or object storage.
+
+## Backup
+For different backend storage types, there are some differences in the data that needs to be backed up.
+
+There are two backup strategies, depending on the configured storage backend:
+- If you use local storage, you need to backup both index metadata and document data
+- If you use object storage, you only need to backup index metadata. Whether and how the document data needs backup depends on your object storage setup.
+
+We assume your `SS_DATA_PATH` is `/opt/seasearch/` and you want to backup to `/backup` directory. 
+
+### Backup strategy for local storage
+
+The data files are all stored in the directory specified by `SS_DATA_PATH` environment variable, so just back up the whole directory. 
+You can directly copy the whole directory to the backup destination, or you can use rsync to do incremental backup.
+
+To directly copy the whole data directory:
+```
+cp -R /opt/seasearch /backup/data/seasearch-`date +"%Y-%m-%d-%H-%M-%S"`
+```
+This produces a separate copy of the data directory each time. You can delete older backup copies after a new one is completed.
+
+If you have a lot of data, copying the whole data directory would take long. You can use rsync to do incremental backup.
+```
+rsync -az /opt/seasearch /backup/data/
+```
+
+This command backup the data directory to `/backup/data/seasearch`.
+
+### Backup strategy for object storage
+
+When SeaSearch is deployed with object storage backend, you only need to back up the metadata file.
+
+To directly copy the metadata file:
+```
+cp /opt/seasearch/_metadata.bolt /backup/data/seasearch-metadata.bolt.`date +"%Y-%m-%d-%H-%M-%S"`
+```
+This produces a separate copy of the data directory each time. You can delete older backup copies after a new one is completed.
+
+## Restore
+
+Now suppose your primary SeaSearch server has failed, and you are switching to a new machine.
+
+Assume that the deployment location of SeaSearch on the new machine is also `/opt/seasearch`, and the backup files are located at `/backup/data/seasearch-2025-01-18-14-35-45`.
+
+### Restore strategy for local storage
+
+You only need to copy the backup data files to the new machine:
+```
+cp -R /backup/data/seasearch-2025-01-18-14-35-45/ /opt/seasearch
+```
+
+### Restore strategy for object storage
+
+Simply copy the backup file to `/opt/seasearch/` and rename it to `_metadata.bolt`:
+
+```
+cp /backup/data/seasearch-metadata.bolt.2025-01-18-14-35-45 /opt/seaserch/_metadata.bolt
+```

mkdocs.yml

@@ -58,6 +58,7 @@ nav:
     - Deploy SeaSearch: usage/deploy.md
     - Use and access SeaSearch APIs: usage/use_and_access_seasearch_apis.md
     - Https: usage/https.md
+    - Backup and Restore: usage/backup_and_restore.md
   - Configuration: config/README.md
   - SeaSearch API: 
     - Overview: api/overview.md