diff --git a/proto/depot/cloud/v3/machine.proto b/proto/depot/cloud/v3/machine.proto
index 52c407b..2b25d74 100644
--- a/proto/depot/cloud/v3/machine.proto
+++ b/proto/depot/cloud/v3/machine.proto
@@ -58,6 +58,8 @@ message RegisterMachineResponse {
       string key = 3;
       // Store at /etc/ceph/ceph.conf
       string ceph_conf = 4;
+      // If the image_spec is set use instead of constructing with the volume_name.
+      string image_spec = 5;
     }
   }
 
diff --git a/src/gen/ts/depot/cloud/v3/machine_pb.ts b/src/gen/ts/depot/cloud/v3/machine_pb.ts
index bb562ea..1cf4181 100644
--- a/src/gen/ts/depot/cloud/v3/machine_pb.ts
+++ b/src/gen/ts/depot/cloud/v3/machine_pb.ts
@@ -377,6 +377,13 @@ export class RegisterMachineResponse_Mount_CephVolume extends Message<RegisterMa
    */
   cephConf = ''
 
+  /**
+   * If the image_spec is set use instead of constructing with the volume_name.
+   *
+   * @generated from field: string image_spec = 5;
+   */
+  imageSpec = ''
+
   constructor(data?: PartialMessage<RegisterMachineResponse_Mount_CephVolume>) {
     super()
     proto3.util.initPartial(data, this)
@@ -389,6 +396,7 @@ export class RegisterMachineResponse_Mount_CephVolume extends Message<RegisterMa
     {no: 2, name: 'client_name', kind: 'scalar', T: 9 /* ScalarType.STRING */},
     {no: 3, name: 'key', kind: 'scalar', T: 9 /* ScalarType.STRING */},
     {no: 4, name: 'ceph_conf', kind: 'scalar', T: 9 /* ScalarType.STRING */},
+    {no: 5, name: 'image_spec', kind: 'scalar', T: 9 /* ScalarType.STRING */},
   ])
 
   static fromBinary(bytes: Uint8Array, options?: Partial<BinaryReadOptions>): RegisterMachineResponse_Mount_CephVolume {
diff --git a/src/tasks/buildkit.ts b/src/tasks/buildkit.ts
index 43b038e..5b0334c 100644
--- a/src/tasks/buildkit.ts
+++ b/src/tasks/buildkit.ts
@@ -220,7 +220,7 @@ keepBytes = ${cacheSizeBytes}
           await fstrim(mount.path)
         }
         await unmountDevice(mount.path)
-        await unmapBlockDevice(mount.cephVolume.volumeName)
+        await unmapBlockDevice(mount.cephVolume.volumeName, mount.cephVolume.imageSpec)
       } else {
         await unmountDevice(mount.path)
       }
diff --git a/src/tasks/engine.ts b/src/tasks/engine.ts
index c72502a..9628a34 100644
--- a/src/tasks/engine.ts
+++ b/src/tasks/engine.ts
@@ -100,7 +100,7 @@ export async function startEngine(message: RegisterMachineResponse, task: Regist
     for (const mount of task.mounts) {
       if (mount.cephVolume) {
         await unmountDevice(mount.path)
-        await unmapBlockDevice(mount.cephVolume.volumeName)
+        await unmapBlockDevice(mount.cephVolume.volumeName, mount.cephVolume.imageSpec)
       } else {
         await unmountDevice(mount.path)
       }
diff --git a/src/utils/mounts.ts b/src/utils/mounts.ts
index f1448f8..38735da 100644
--- a/src/utils/mounts.ts
+++ b/src/utils/mounts.ts
@@ -64,13 +64,13 @@ async function attachCeph(cephVolume: RegisterMachineResponse_Mount_CephVolume):
     }
   } catch {}
 
-  console.log(`Attaching ceph ${volumeName} for ${clientName}`)
+  // Temporarily continue to use the volumeName until we switch entirely to imageSpec.
+  const imageSpec = cephVolume.imageSpec ? cephVolume.imageSpec : `rbd/${volumeName}/${volumeName}`
 
+  console.log(`Attaching ceph ${imageSpec} for ${clientName}`)
+  const keyringPath = `/etc/ceph/ceph.${clientName}.keyring`
   // NOTE: The API sends the device name as `/dev/rbd/rbd/${volumeName}/${volumeName}`
   // This means we ignore the device name returned from mapping.
-
-  const imageSpec = `rbd/${volumeName}/${volumeName}`
-  const keyringPath = `/etc/ceph/ceph.${clientName}.keyring`
   await execa('rbd', ['map', imageSpec, '--name', clientName, '--keyring', keyringPath], {stdio: 'inherit'})
   console.log(`Mapped ${imageSpec}`)
   const device = await getCephDeviceName(cephVolume)
@@ -202,8 +202,11 @@ async function writeCephConf(clientName: string, cephConf: string, key: string)
   await fsp.chmod(keyringPath, 0o600)
 }
 
-export async function unmapBlockDevice(volumeName: string) {
-  const imageSpec = `rbd/${volumeName}/${volumeName}`
+export async function unmapBlockDevice(volumeName: string, imageSpec?: string) {
+  // Temporarily continue to use the volumeName until we switch entirely to imageSpec.
+  if (!imageSpec) {
+    imageSpec = `rbd/${volumeName}/${volumeName}`
+  }
   const {exitCode, stderr} = await execa('rbd', ['unmap', imageSpec], {reject: false, stdio: 'inherit'})
   console.log(`Unmapped ${imageSpec} with exit code ${exitCode}`)
   // 22 means that the device is not mapped a.k.a EINVAL.