Document Storage Rollback mechanism

Updated Rake-specific documentation to include storage rollback,
and improved migration and rollback instructions.

1 files changed, 45 insertions, 3 deletions

diff --git a/doc/administration/raketasks/storage.md b/doc/administration/raketasks/storage.md
index 7ad38abe4f5..c39fef907db 100644
--- a/doc/administration/raketasks/storage.md
+++ b/doc/administration/raketasks/storage.md
@@ -34,17 +34,59 @@ export ID_FROM=20
 export ID_TO=50
 ```
 
-You can monitor the progress in the _Admin > Monitoring > Background jobs_ screen.
-There is a specific Queue you can watch to see how long it will take to finish: **project_migrate_hashed_storage**
+You can monitor the progress in the **Admin Area > Monitoring > Background Jobs** page.
+There is a specific Queue you can watch to see how long it will take to finish: 
+`hashed_storage:hashed_storage_project_migrate`
 
 After it reaches zero, you can confirm every project has been migrated by running the commands bellow. 
 If you find it necessary, you can run this migration script again to schedule missing projects.
 
-Any error or warning will be logged in the sidekiq's log file.
+Any error or warning will be logged in Sidekiq's log file.
 
 You only need the `gitlab:storage:migrate_to_hashed` rake task to migrate your repositories, but we have additional
 commands below that helps you inspect projects and attachments in both legacy and hashed storage.
 
+## Rollback from Hashed storage to Legacy storage
+
+If you need to rollback the storage migration for any reason, you can follow the steps described here.
+
+NOTE: **Note:** Hashed Storage will be required in future version of GitLab.
+
+To prevent new projects from being created in the Hashed storage, 
+you need to undo the [enable hashed storage][storage-migration] changes.
+
+This task will schedule all your existing projects and associated attachments to be rolled back to the
+Legacy storage type.
+
+For Omnibus installations, run the following:
+
+```bash
+sudo gitlab-rake gitlab:storage:rollback_to_legacy
+```
+
+For source installations, run the following:
+
+```bash
+sudo -u git -H bundle exec rake gitlab:storage:rollback_to_legacy RAILS_ENV=production
+```
+
+Both commands accept a range as environment variable:
+
+```bash
+# to rollback any migrated project from ID 20 to 50.
+export ID_FROM=20 
+export ID_TO=50
+```
+
+You can monitor the progress in the **Admin Area > Monitoring > Background Jobs** page.
+On the **Queues** tab, you can watch the `hashed_storage:hashed_storage_project_rollback` queue to see how long the process will take to finish.
+
+
+After it reaches zero, you can confirm every project has been rolled back by running the commands bellow. 
+If some projects weren't rolled back, you can run this rollback script again to schedule further rollbacks.
+
+Any error or warning will be logged in Sidekiq's log file.
+
 ## List projects on Legacy storage
 
 To have a simple summary of projects using **Legacy** storage: