---
metadata:
  - name: generator
    content: Diplodoc Platform v5.52.0
alternate:
  - https://ydb.tech/docs/en/devops/deployment-options/manual/decommissioning.md?version=v25.4
  - https://ydb.tech/docs/ru/devops/deployment-options/manual/decommissioning.md?version=v25.4
  - href: en/devops/deployment-options/manual/decommissioning.md
    type: text/markdown
    title: Markdown version
  - href: ../../../llms.txt
    type: text/markdown
    title: llms.txt
sourcePath: en/core/devops/deployment-options/manual/decommissioning.md
---
> **Documentation Index:** Fetch the complete configuration index at https://ydb.tech/docs/en/llms.txt

# Data Center Decommissioning

{% note info %}

Use this procedure only to decommission an entire data center.

{% endnote %}

Decommissioning is the procedure for moving a VDisk from a PDisk that needs to be decommissioned.

Data is moved to PDisk clusters where there is enough free space to create new slots. Moving is performed only when there is a possibility of moving with at least partial preservation of the failure model. It may happen that the system can't strictly follow the failure model during decommissioning. However, it does its best to ensure fault-tolerance as fully as under normal operation. For example, when encoding `mirror-3-dc`, a situation may arise when a group is located in four rather than three data centers.

Decommissioning is done asynchronously, meaning that data is not moved immediately while handling the command. If the failure model allows, SelfHeal moves slots one by one in the background to completely release the specified PDisks.

## Managing Decommission {#decommitstatus}

To manage the state of decommissioning, set the `DecommitStatus` parameter for the appropriate PDisk. The parameter can take the following values:

* `DECOMMIT_NONE`: The disk is not being decommissioned and is running normally, according to its condition.
* `DECOMMIT_PENDING`: Disk decommissioning is scheduled. Data is not transferred from the disk. However, slots for new groups won't be created and the slots of the previously created groups won't be moved.
* `DECOMMIT_IMMINENT`: Disk decommissioning is required. Data is transferred in the background to disks that have the `DECOMMIT_NONE` status and satisfy the failure model.

The `DECOMMIT_PENDING` and `DECOMMIT_IMMINENT` values shouldn't be removed under normal decommissioning, since the equipment is removed from the cluster by running the `DefineBox` command.

To cancel decommissioning, just change the disk status to `DECOMMIT_NONE`. In this case, BS_CONTROLLER won't take any additional actions: the previously moved VDisks remain where they are. To return them, you can use commands to move slots point by point, depending on the specific situation.

By managing the `DECOMMIT_PENDING` and `DECOMMIT_IMMINENT` states, you can perform cluster decommissioning in parts.

For example, you need to move equipment from data center-1 (DC-1) to data center-2 (DC-2):

1. The DC-2 hosts buffer equipment to transfer the first chunk of data to.
1. Switch the status of all DC-1 disks to `DECOMMIT_PENDING` at once so that no data can be moved inside the DC-1. Set this status for every disk in the data center simultaneously: applying `DECOMMIT_PENDING` to only a subset of disks in the data center may cause violation of the storage group failure model.
1. Switch the status of all DC-1 disks to `DECOMMIT_IMMINENT` on the equipment that is equivalent to the buffer one.
1. Wait until all the disks in the `DECOMMIT_IMMINENT` status are released.
1. Move the released equipment from the DC-1 to the DC-2 and switch the status of its disks to `DECOMMIT_NONE`.

Repeat the above steps for the next set of equipment in the DC-1 until all the equipment is moved.

To set the desired state of disk decommissioning, use the [YDB DSTool](https://ydb.tech/docs/en/reference/ydb-dstool/index.md?version=v25.4) utility. The command below sets the `DECOMMIT_IMMINENT` status for the disk with the ID `1000` on the node with the ID `1`:

```bash
ydb-dstool -e  <bs_endpoint> pdisk set --decommit-status DECOMMIT_IMMINENT --pdisk-ids "[1:1000]"
```