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# Recovery options
Gitaly Cluster can [recover from certain types of failure](recovery.md).
## Primary Node Failure
Gitaly Cluster recovers from a failing primary Gitaly node by promoting a healthy secondary as the
new primary.
In GitLab 14.1 and later, Gitaly Cluster:
- Elects a healthy secondary with a fully up to date copy of the repository as the new primary.
- Repository becomes unavailable if there are no fully up to date copies of it on healthy secondaries.
To minimize data loss in GitLab 13.0 to 14.0, Gitaly Cluster:
- Switches repositories that are outdated on the new primary to [read-only mode](#read-only-mode).
- Elects the secondary with the least unreplicated writes from the primary to be the new
primary. Because there can still be some unreplicated writes,
> - Between GitLab 13.0 and GitLab 13.2, read-only mode applied to the whole virtual storage and occurred whenever failover occurred.
> - [In GitLab 13.3 and later](https://gitlab.com/gitlab-org/gitaly/-/issues/2862), read-only mode applies on a per-repository basis and only occurs if a new primary is out of date.
new primary. If the failed primary contained unreplicated writes, [data loss can occur](#check-for-data-loss).
> - Removed in GitLab 14.1. Instead, repositories [become unavailable](#unavailable-repositories).
When Gitaly Cluster switches to a new primary in GitLab 13.0 to 14.0, repositories enter
read-only mode if they are out of date. This can happen after failing over to an outdated
secondary. Read-only mode eases data recovery efforts by preventing writes that may conflict
with the unreplicated writes on other nodes.
To enable writes again in GitLab 13.0 to 14.0, an administrator can:
1. [Check](#check-for-data-loss) for data loss.
1. Attempt to [recover](#data-recovery) missing data.
1. Either [enable writes](#enable-writes-or-accept-data-loss) in the virtual storage or
[accept data loss](#enable-writes-or-accept-data-loss) if necessary, depending on the version of
GitLab.
## Unavailable repositories
> - From GitLab 13.0 through 14.0, repositories became read-only if they were outdated on the primary but fully up to date on a healthy secondary. `dataloss` sub-command displays read-only repositories by default through these versions.
> - Since GitLab 14.1, Praefect contains more responsive failover logic which immediately fails over to one of the fully up to date secondaries rather than placing the repository in read-only mode. Since GitLab 14.1, the `dataloss` sub-command displays repositories which are unavailable due to having no fully up to date copies on healthy Gitaly nodes.
A repository is unavailable if all of its up to date replicas are unavailable. Unavailable repositories are
not accessible through Praefect to prevent serving stale data that may break automated tooling.
### Check for data loss
The Praefect `dataloss` subcommand identifies:
- Copies of repositories in GitLab 13.0 to GitLab 14.0 that at are likely to be outdated.
This can help identify potential data loss after a failover.
- Repositories in GitLab 14.1 and later that are unavailable. This helps identify potential
data loss and repositories which are no longer accessible because all of their up-to-date
replicas copies are unavailable.
The following parameters are available:
-`-virtual-storage` that specifies which virtual storage to check. Because they might require
an administrator to intervene, the default behavior is to display:
- In GitLab 13.0 to 14.0, copies of read-only repositories.
- In GitLab 14.1 and later, unavailable repositories.
- In GitLab 14.1 and later, [`-partially-unavailable`](#unavailable-replicas-of-available-repositories)
that specifies whether to include in the output repositories that are available but have
-`-virtual-storage` is the virtual storage the repository is located in. Virtual storages are configured in `/etc/gitlab/gitlab.rb` under `praefect['virtual_storages]` and looks like the following:
```ruby
praefect['virtual_storages'] = {
'default' => {
...
},
'storage-1' => {
...
}
}
```
In this example, the virtual storage to specify is `default` or `storage-1`.
-`-repository` is the repository's relative path in the storage [beginning with `@hashed`](../repository_storage_types.md#hashed-storage).
-`-virtual-storage` is the virtual storage the repository is located in. Virtual storages are configured in `/etc/gitlab/gitlab.rb` under `praefect['virtual_storages]` and looks like the following:
```ruby
praefect['virtual_storages'] = {
'default' => {
...
},
'storage-1' => {
...
}
}
```
In this example, the virtual storage to specify is `default` or `storage-1`.
-`-repository` is the repository's relative path in the storage [beginning with `@hashed`](../repository_storage_types.md#hashed-storage).
