PSMDB-1284 Doc: File copy based initial sync

docs/initial-sync.md

@@ -0,0 +1,26 @@
+# File copy based initial sync
+
+!!! admonition "Version added: [7.0.21-12](release_notes/7.0.21-12.md)"
+
+When a new member joins the replica set, it receives the data from the existing replica set node via the initial sync. 
+
+The default initial sync method is logical, during which Percona Server for MongoDB clones all databases except the `local` database, builds all collection indexes, pulls oplog records and applies the changes to the data set. Read more about [logical initial sync in MongoDB documentation](https://www.mongodb.com/docs/manual/core/replica-set-sync/#logical-initial-sync-process).
+
+Starting with version 7.0.21-12, you can select **file copy based** as the initial sync method. You must have the WiredTiger storage defined in Percona Server for MongoDB configuration. File copy based initial sync is the physical copying of the data files from source to target. This sync method is faster than logical, which is especially beneficial in heavy write environments. It speeds up cluster scaling and increases restore performance.
+
+File copy-based initial sync is implemented in a similar way as in MongoDB Advanced and has the same configuration options. For workflow and known limitations, refer to [MongoDB documentation](https://www.mongodb.com/docs/manual/core/replica-set-sync/#file-copy-based-initial-sync). 
+
+To select the initial sync method, specify the following configuration in the configuration file for the target server:
+
+```yaml
+setParameter:
+  initialSyncMethod: fileCopyBased
+```
+
+You can only set this configuration at startup.
+
+
+File copy based initial sync is available in [Percona Server for MongoDB Pro out of the box](psmdb-pro.md). You can also receive this functionality by [building Percona Server for MongoDB from source code](install/source.md). 
+
+
+

docs/psmdb-pro.md

@@ -15,6 +15,7 @@ Find the list of solutions available in Percona Server for MongoDB Pro builds:
 | Name                                | Version added | Description  | 
 | ----------------------------------- | ------------- | -------------
 | [FIPS support ](fips.md)| [7.0.4-2](release_notes/7.0.4-2.md) | FIPS mode provides a way to use FIPS-compliant encryption and run the Percona Server for MongoDB with the FIPS-140 certified library for OpenSSL. This helps customers meet minimum security requirements for cryptographic modules and testing in both hardware and software. |
+| [File copy based initial sync](initial-sync.md) | [7.0.21-12](release_notes/7.0.21-12.md) | File copy based initial sync is a new method of syncing data between nodes in a cluster. It is faster than the logical sync method as it copies physical files rather than cloning data. |
 
 ## Benefits
 

mkdocs-base.yml

@@ -195,6 +195,7 @@ nav:
         - "Use local keyfile": keyfile.md
         - "Migrate from keyfile to Vault": encryption-mode-switch.md
         - fips.md
+      - initial-sync.md
       - audit-logging.md 
       - rate-limit.md
       - log-redaction.md