Add storage size information

doc/administration/gitaly/index.md

@@ -213,7 +213,9 @@ In this example:
 - Each repository is stored on one of three Gitaly storages: `storage-1`, `storage-2`,
   or `storage-3`.
 - Each storage is serviced by a Gitaly node.
-- The three Gitaly nodes store data in three separate hashed storage locations.
+- The three Gitaly nodes share data in three separate hashed storage locations.
+- The [replication factor](praefect.md#replication-factor) is `3`. There are three copies maintained
+  of each repository.
 
 Generally, virtual storage with Gitaly Cluster can replace direct Gitaly storage configurations, at
 the expense of additional storage needed to store each repository on multiple Gitaly nodes. The

doc/administration/gitaly/praefect.md

@@ -7,9 +7,14 @@ type: reference
 
 # Configure Gitaly Cluster **(FREE SELF)**
 
-In addition to Gitaly Cluster configuration instructions available as part of
-[reference architectures](../reference_architectures/index.md) for installations for more than
-2000 users, advanced configuration instructions are available below.
+Configure Gitaly Cluster using either:
+
+- The Gitaly Cluster configuration instructions available as part of
+  [reference architectures](../reference_architectures/index.md) for installations for more than
+  2000 users.
+- The advanced configuration instructions that follow on this page.
+
+Smaller GitLab installations may need only [Gitaly itself](index.md).
 
 ## Requirements for configuring a Gitaly Cluster
 
@@ -1004,7 +1009,7 @@ replication factor offers better redundancy and distribution of read workload, b
 in a higher storage cost. By default, Praefect replicates repositories to every storage in a
 virtual storage.
 
-### Configure replication factors
+### Configure replication factor
 
 WARNING:
 The feature is not production ready yet. After you set a replication factor, you can't unset it
@@ -1298,6 +1303,25 @@ sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.t
 
 ## Migrate to Gitaly Cluster
 
+Whether migrating to Gitaly Cluster because of [NFS support deprecation](index.md#nfs-deprecation-notice)
+or to move from single Gitaly nodes, the basic process involves:
+
+1. Create the required storage.
+1. Create and configure Gitaly Cluster.
+1. [Move the repositories](#move-repositories).
+
+The size of the required storage can vary between instances and depends on the set
+[replication factor](#replication-factor). The migration to Gitaly Cluster might include
+implementing repository storage redundancy.
+
+For a replication factor:
+
+- Of `1`: NFS, Gitaly, and Gitaly Cluster have roughly the same storage requirements.
+- More than `1`: The amount of required storage is `used space * replication factor`. `used space`
+  should include any planned future growth.
+
+### Move Repositories
+
 To migrate to Gitaly Cluster, existing repositories stored outside Gitaly Cluster must be
 moved. There is no automatic migration but the moves can be scheduled with the GitLab API.
 
@@ -1316,11 +1340,11 @@ After creating and configuring Gitaly Cluster:
    so that the Gitaly Cluster receives all new projects. This stops new projects being created
    on existing Gitaly nodes while the migration is in progress.
 1. Schedule repository moves for:
-   - [Projects](#bulk-schedule-projects).
-   - [Snippets](#bulk-schedule-snippets).
-   - [Groups](#bulk-schedule-groups). **(PREMIUM SELF)**
+   - [Projects](#bulk-schedule-project-moves).
+   - [Snippets](#bulk-schedule-snippet-moves).
+   - [Groups](#bulk-schedule-group-moves). **(PREMIUM SELF)**
 
-### Bulk schedule projects
+#### Bulk schedule project moves
 
 1. [Schedule repository storage moves for all projects on a storage shard](../../api/project_repository_storage_moves.md#schedule-repository-storage-moves-for-all-projects-on-a-storage-shard) using the API. For example:
 
@@ -1353,7 +1377,7 @@ After creating and configuring Gitaly Cluster:
 
 1. Repeat for each storage as required.
 
-### Bulk schedule snippets
+#### Bulk schedule snippet moves
 
 1. [Schedule repository storage moves for all snippets on a storage shard](../../api/snippet_repository_storage_moves.md#schedule-repository-storage-moves-for-all-snippets-on-a-storage-shard) using the API. For example:
 
@@ -1378,7 +1402,7 @@ After creating and configuring Gitaly Cluster:
 
 1. Repeat for each storage as required.
 
-### Bulk schedule groups **(PREMIUM SELF)**
+#### Bulk schedule group moves **(PREMIUM SELF)**
 
 1. [Schedule repository storage moves for all groups on a storage shard](../../api/group_repository_storage_moves.md#schedule-repository-storage-moves-for-all-groups-on-a-storage-shard) using the API.