Note about issues with storage migration

doc/update/index.md

@@ -177,14 +177,14 @@ Find where your version sits in the upgrade path below, and upgrade GitLab
 accordingly, while also consulting the
 [version-specific upgrade instructions](#version-specific-upgrading-instructions):
 
-`8.11.Z` -> `8.12.0` -> `8.17.7` -> `9.5.10` -> `10.8.7` -> `11.11.8` -> `12.0.12` -> `12.1.17` -> `12.10.14` -> `13.0.14` -> `13.1.11` - > [latest `13.Y.Z`](https://about.gitlab.com/releases/categories/releases/)
+`8.11.Z` -> `8.12.0` -> `8.17.7` -> `9.5.10` -> `10.8.7` -> `11.11.8` -> `12.0.12` -> `12.1.17` -> `12.10.14` -> `13.0.14` -> `13.1.11`  -> `13.5.4` - > [latest `13.Y.Z`](https://about.gitlab.com/releases/categories/releases/)
 
 The following table, while not exhaustive, shows some examples of the supported
 upgrade paths.
 
 | Target version | Your version | Supported upgrade path | Note |
 | --------------------- | ------------ | ------------------------ | ---- |
-| `13.4.3`                | `12.9.2`      | `12.9.2` -> `12.10.14` -> `13.0.14` -> `13.4.3` | Two intermediate versions are required: the final `12.10` release, plus `13.0`. |
+| `13.5.4`                | `12.9.2`      | `12.9.2` -> `12.10.14` -> `13.0.14`  -> `13.1.11` -> `13.5.4` | Three intermediate versions are required: the final `12.10` release, plus `13.0` and `13.1`. |
 | `13.2.10`                | `11.5.0`      | `11.5.0` -> `11.11.8` -> `12.0.12` -> `12.1.17` -> `12.10.14` -> `13.0.14` -> `13.2.10` | Five intermediate versions are required: the final `11.11`, `12.0`, `12.1` and `12.10` releases, plus `13.0`. |
 | `12.10.14`             | `11.3.4`       | `11.3.4` -> `11.11.8` -> `12.0.12` -> `12.1.17` -> `12.10.14`             |  Three intermediate versions are required: the final `11.11` and `12.0` releases, plus `12.1` |
 | `12.9.5`             | `10.4.5`       | `10.4.5` -> `10.8.7` -> `11.11.8` -> `12.0.12` -> `12.1.17` -> `12.9.5`   | Four intermediate versions are required: `10.8`, `11.11`, `12.0` and `12.1`, then `12.9.5` |
@@ -358,6 +358,10 @@ Ruby 2.7.2 is required. GitLab will not start with Ruby 2.6.6 or older versions.
 
 The required Git version is Git v2.29 or higher.
 
+### 13.4.0
+
+GitLab 13.4.0 includes a background migration to [move all remaining repositories in legacy storage to hashed storage](../administration/raketasks/storage.md#migrate-to-hashed-storage). There are [known issues with this migration](https://gitlab.com/gitlab-org/gitlab/-/issues/259605) which are fixed in GitLab 13.5.4 and later. If possible, skip 13.4.0 and upgrade to 13.5.4 or higher instead. Note that the migration can take quite a while to run, depending on how many repositories must be moved. Be sure to check that all background migrations have completed before upgrading further.
+
 ### 13.3.0
 
 The recommended Git version is Git v2.28. The minimum required version of Git