# Attaching Volumes

The following sequence diagram outlines the current flow when attaching a volume to an instance using the `os-volume_attachments` API. This diagram uses the `libvirt` driver as an example virt driver to additionally document the optional interactions with the `os-brick` library on the compute hosts during the request.

Note

`os-brick` is not always used to connect volumes to the host, most notibly when connecting an instance natively to ceph `rbd` volumes

The diagram also outlines the various locks taken on the compute during the attach volume flow. In this example these include locks against the `instance.uuid`, `cinder_backend.uuid` orchestrated for `nova-compute` by `os-brick` and the generic `connect_volume` lock taken within os-brick itself. This final `connect_volume` lock also being held when detaching and disconnecting a volume from the host by `os-brick`.

this page last updated: 2026-06-10 20:07:09

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