Improvement: restructure backups pages

docs/operations_/backup_restore/01_local_disk.md

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+---
+description: 'Details backup/restore to or from a local disk'
+sidebar_label: 'Local disk / S3 disk'
+slug: /operations/backup/disk
+title: 'Backup and Restore in ClickHouse'
+doc_type: 'guide'
+---
+
+import GenericSettings from '@site/docs/operations_/backup_restore/_snippets/_generic_settings.md';
+import S3Settings from '@site/docs/operations_/backup_restore/_snippets/_s3_settings.md';
+import ExampleSetup from '@site/docs/operations_/backup_restore/_snippets/_example_setup.md';
+import Syntax from '@site/docs/operations_/backup_restore/_snippets/_syntax.md';
+
+# BACKUP / RESTORE to disk {#backup-to-a-local-disk}
+
+## Syntax {#syntax}
+
+<Syntax/>
+
+## Configure backup destinations for disk {#configure-backup-destinations-for-disk}
+
+### Configure a backup destination for local disk {#configure-a-backup-destination}
+
+In the examples below you will see the backup destination specified as `Disk('backups', '1.zip')`.  
+To use the `Disk` backup engine it is necessary to first add a file specifying 
+the backup destination at the path below:
+
+```text
+/etc/clickhouse-server/config.d/backup_disk.xml
+```
+
+For example, the configuration below defines a disk named `backups` and then adds that disk to
+the **allowed_disk** list of **backups**:
+
+```xml
+<clickhouse>
+    <storage_configuration>
+        <disks>
+<!--highlight-next-line -->
+            <backups>
+                <type>local</type>
+                <path>/backups/</path>
+            </backups>
+        </disks>
+    </storage_configuration>
+<!--highlight-start -->
+    <backups>
+        <allowed_disk>backups</allowed_disk>
+        <allowed_path>/backups/</allowed_path>
+    </backups>
+<!--highlight-end -->
+</clickhouse>
+```
+
+### Configure a backup destination for S3 disk {#backuprestore-using-an-s3-disk}
+
+It is also possible to `BACKUP`/`RESTORE` to S3 by configuring an S3 disk in the
+ClickHouse storage configuration. Configure the disk like this by adding a file to
+`/etc/clickhouse-server/config.d` as was done above for the local disk.
+
+```xml
+<clickhouse>
+    <storage_configuration>
+        <disks>
+            <s3_plain>
+                <type>s3_plain</type>
+                <endpoint></endpoint>
+                <access_key_id></access_key_id>
+                <secret_access_key></secret_access_key>
+            </s3_plain>
+        </disks>
+        <policies>
+            <s3>
+                <volumes>
+                    <main>
+                        <disk>s3_plain</disk>
+                    </main>
+                </volumes>
+            </s3>
+        </policies>
+    </storage_configuration>
+
+    <backups>
+        <allowed_disk>s3_plain</allowed_disk>
+    </backups>
+</clickhouse>
+```
+
+`BACKUP`/`RESTORE` for S3 disk is done in the same way as for local disk:
+
+```sql
+BACKUP TABLE data TO Disk('s3_plain', 'cloud_backup');
+RESTORE TABLE data AS data_restored FROM Disk('s3_plain', 'cloud_backup');
+```
+
+:::note
+- This disk should not be used for `MergeTree` itself, only for `BACKUP`/`RESTORE`
+- If your tables are backed by S3 storage and the types of the disks are different, 
+it doesn't use `CopyObject` calls to copy parts to the destination bucket, instead,
+it downloads and uploads them, which is very inefficient. In this case prefer using
+the `BACKUP ... TO S3(<endpoint>)` syntax for this use-case.
+:::
+
+## Usage examples of backup/restore to local disk {#usage-examples}
+
+### Backup and restore a table {#backup-and-restore-a-table}
+
+<ExampleSetup/>
+
+To backup the table you can run:
+
+```sql title="Query"
+BACKUP TABLE test_db.test_table TO Disk('backups', '1.zip')
+```
+
+```response title="Response"
+   ┌─id───────────────────────────────────┬─status─────────┐
+1. │ 065a8baf-9db7-4393-9c3f-ba04d1e76bcd │ BACKUP_CREATED │
+   └──────────────────────────────────────┴────────────────┘
+```
+
+The table can be restored from the backup using the following command if the table is empty:
+
+```sql title="Query"
+RESTORE TABLE test_db.test_table FROM Disk('backups', '1.zip')
+```
+
+```response title="Response"
+   ┌─id───────────────────────────────────┬─status───┐
+1. │ f29c753f-a7f2-4118-898e-0e4600cd2797 │ RESTORED │
+   └──────────────────────────────────────┴──────────┘
+```
+
+:::note
+The above `RESTORE` would fail if the table `test.table` contains data.
+The setting `allow_non_empty_tables=true` allows `RESTORE TABLE` to insert data
+into non-empty tables. This will mix earlier data in the table with the data extracted from the backup.
+This setting can therefore cause data duplication in the table, and should be used with caution.
+:::
+
+To restore the table with data already in it, run:
+
+```sql
+RESTORE TABLE test_db.table_table FROM Disk('backups', '1.zip')
+SETTINGS allow_non_empty_tables=true
+```
+
+Tables can be restored, or backed up, with new names:
+
+```sql
+RESTORE TABLE test_db.table_table AS test_db.test_table_renamed FROM Disk('backups', '1.zip')
+```
+
+The backup archive for this backup has the following structure:
+
+```text
+├── .backup
+└── metadata
+    └── test_db
+        └── test_table.sql
+```
+
+<!-- TO DO: 
+Explanation here about the backup format. See Issue 24a
+https://github.com/ClickHouse/clickhouse-docs/issues/3968
+--> 
+
+Formats other than zip can be used. See ["Backups as tar archives"](#backups-as-tar-archives)
+below for further details.
+
+### Incremental backups to disk {#incremental-backups}
+
+A base backup in ClickHouse is the initial, full backup from which the following 
+incremental backups are created. Incremental backups only store the changes 
+made since the base backup, so the base backup must be kept available to
+restore from any incremental backup. The base backup destination can be set with setting
+`base_backup`.
+
+:::note
+Incremental backups depend on the base backup. The base backup must be kept available 
+to be able to restore from an incremental backup.
+:::
+
+To make an incremental backup of a table, first make a base backup:
+
+```sql
+BACKUP TABLE test_db.test_table TO Disk('backups', 'd.zip')
+```
+
+```sql
+BACKUP TABLE test_db.test_table TO Disk('backups', 'incremental-a.zip')
+SETTINGS base_backup = Disk('backups', 'd.zip')
+```
+
+All data from the incremental backup and the base backup can be restored into a
+new table `test_db.test_table2` with command:
+
+```sql
+RESTORE TABLE test_db.test_table AS test_db.test_table2
+FROM Disk('backups', 'incremental-a.zip');
+```
+
+### Securing a backup {#assign-a-password-to-the-backup}
+
+Backups written to disk can have a password applied to the file.
+The password can be specified using the `password` setting:
+
+```sql
+BACKUP TABLE test_db.test_table
+TO Disk('backups', 'password-protected.zip')
+SETTINGS password='qwerty'
+```
+
+To restore a password-protected backup, the password must again
+be specified using the `password` setting:
+
+```sql
+RESTORE TABLE test_db.test_table
+FROM Disk('backups', 'password-protected.zip')
+SETTINGS password='qwerty'
+```
+
+### Backups as tar archives {#backups-as-tar-archives}
+
+Backups can be stored not only as zip archives, but also as tar archives. 
+The functionality is the same as for zip, except that password protection is not 
+supported for tar archives. Additionally, tar archives support a variety of 
+compression methods.
+
+To make a backup of a table as a tar:
+
+```sql
+BACKUP TABLE test_db.test_table TO Disk('backups', '1.tar')
+```
+
+to restore from a tar archive:
+
+```sql
+RESTORE TABLE test_db.test_table FROM Disk('backups', '1.tar')
+```
+
+To change the compression method, the correct file suffix should be appended to 
+the backup name. For example, to compress the tar archive using gzip run:
+
+```sql
+BACKUP TABLE test_db.test_table TO Disk('backups', '1.tar.gz')
+```
+
+The supported compression file suffixes are:
+- `tar.gz`
+- `.tgz`
+- `tar.bz2`
+- `tar.lzma`
+- `.tar.zst`
+- `.tzst`
+- `.tar.xz`
+
+### Compression settings {#compression-settings}
+
+The compression method and level of compression can be specified using
+setting `compression_method` and `compression_level` respectively.
+
+<!-- TO DO:
+More information needed on these settings and why you would want to do this 
+-->
+
+```sql
+BACKUP TABLE test_db.test_table
+TO Disk('backups', 'filename.zip')
+SETTINGS compression_method='lzma', compression_level=3
+```
+
+### Restore specific partitions {#restore-specific-partitions}
+
+If specific partitions associated with a table need to be restored, these can be specified.
+
+Let's create a simple partitioned table into four parts, insert some data into it and then
+take a backup of only the first and fourth partitions:
+
+<details>
+
+<summary>Setup</summary>
+
+```sql
+CREATE IF NOT EXISTS test_db;
+
+-- Create a partitioend table
+CREATE TABLE test_db.partitioned (
+    id UInt32,
+    data String,
+    partition_key UInt8
+) ENGINE = MergeTree()
+PARTITION BY partition_key
+ORDER BY id;
+
+INSERT INTO test_db.partitioned VALUES
+(1, 'data1', 1),
+(2, 'data2', 2),
+(3, 'data3', 3),
+(4, 'data4', 4);
+
+SELECT count() FROM test_db.partitioned;
+
+SELECT partition_key, count() 
+FROM test_db.partitioned
+GROUP BY partition_key
+ORDER BY partition_key;
+```
+
+```response
+   ┌─count()─┐
+1. │       4 │
+   └─────────┘
+   ┌─partition_key─┬─count()─┐
+1. │             1 │       1 │
+2. │             2 │       1 │
+3. │             3 │       1 │
+4. │             4 │       1 │
+   └───────────────┴─────────┘
+```
+
+</details>
+
+Run the following command to back up partitions 1 and 4:
+
+```sql
+BACKUP TABLE test_db.partitioned PARTITIONS '1', '4'
+TO Disk('backups', 'partitioned.zip')
+```
+
+Run the following command to restore partitions 1 and 4:
+
+```sql
+RESTORE TABLE test_db.partitioned PARTITIONS '1', '4'
+FROM Disk('backups', 'partitioned.zip')
+SETTINGS allow_non_empty_tables=true
+```