diff --git a/src/xo-mixins/xen-servers.js b/src/xo-mixins/xen-servers.js
new file mode 100644
index 000000000..cfa80301a
--- /dev/null
+++ b/src/xo-mixins/xen-servers.js
@@ -0,0 +1,355 @@
+import Xapi from '../xapi'
+import xapiObjectToXo from '../xapi-object-to-xo'
+import XapiStats from '../xapi-stats'
+import {
+  JsonRpcError,
+  NoSuchObject
+} from '../api-errors'
+import {
+  camelToSnakeCase,
+  createRawObject,
+  forEach,
+  isEmpty,
+  isString,
+  noop,
+  popProperty
+} from '../utils'
+import {
+  Servers
+} from '../models/server'
+
+// ===================================================================
+
+class NoSuchXenServer extends NoSuchObject {
+  constructor (id) {
+    super(id, 'xen server')
+  }
+}
+
+// ===================================================================
+
+export default class {
+  constructor (xo) {
+    this._objectConflicts = createRawObject() // TODO: clean when a server is disconnected.
+    this._servers = new Servers({
+      connection: xo._redis,
+      prefix: 'xo:server',
+      indexes: ['host']
+    })
+    this._stats = new XapiStats()
+    this._xapis = createRawObject()
+    this._xo = xo
+
+    xo.on('start', async () => {
+      // Connects to existing servers.
+      const servers = await this._servers.get()
+      for (let server of servers) {
+        if (server.enabled) {
+          this.connectXenServer(server.id).catch(error => {
+            console.error(
+              `[WARN] ${server.host}:`,
+              error[0] || error.stack || error.code || error
+            )
+          })
+        }
+      }
+    })
+
+    // TODO: disconnect servers on stop.
+  }
+
+  async registerXenServer ({host, username, password, readOnly = false}) {
+    // FIXME: We are storing passwords which is bad!
+    //        Could we use tokens instead?
+    // TODO: use plain objects
+    const server = await this._servers.create({
+      host,
+      username,
+      password,
+      readOnly: readOnly ? 'true' : undefined,
+      enabled: 'true'
+    })
+
+    return server.properties
+  }
+
+  async unregisterXenServer (id) {
+    this.disconnectXenServer(id).catch(noop)
+
+    if (!await this._servers.remove(id)) { // eslint-disable-line space-before-keywords
+      throw new NoSuchXenServer(id)
+    }
+  }
+
+  async updateXenServer (id, {host, username, password, readOnly, enabled}) {
+    const server = await this._getXenServer(id)
+
+    if (host) server.set('host', host)
+    if (username) server.set('username', username)
+    if (password) server.set('password', password)
+
+    if (enabled !== undefined) {
+      server.set('enabled', enabled ? 'true' : undefined)
+    }
+
+    if (readOnly !== undefined) {
+      server.set('readOnly', readOnly ? 'true' : undefined)
+      const xapi = this._xapis[id]
+      if (xapi) {
+        xapi.readOnly = readOnly
+      }
+    }
+
+    await this._servers.update(server)
+  }
+
+  // TODO: this method will no longer be async when servers are
+  // integrated to the main collection.
+  async _getXenServer (id) {
+    const server = await this._servers.first(id)
+    if (!server) {
+      throw new NoSuchXenServer(id)
+    }
+
+    return server
+  }
+
+  _onXenAdd (xapiObjects, xapiIdsToXo, toRetry, conId) {
+    const conflicts = this._objectConflicts
+    const objects = this._xo._objects
+
+    forEach(xapiObjects, (xapiObject, xapiId) => {
+      try {
+        const xoObject = xapiObjectToXo(xapiObject)
+        if (!xoObject) {
+          return
+        }
+
+        const xoId = xoObject.id
+        xapiIdsToXo[xapiId] = xoId
+
+        const previous = objects.get(xoId, undefined)
+        if (
+          previous &&
+          previous._xapiRef !== xapiObject.$ref
+        ) {
+          (
+            conflicts[xoId] ||
+            (conflicts[xoId] = createRawObject())
+          )[conId] = xoObject
+        } else {
+          objects.set(xoId, xoObject)
+        }
+      } catch (error) {
+        console.error('ERROR: xapiObjectToXo', error)
+
+        toRetry[xapiId] = xapiObject
+      }
+    })
+  }
+
+  _onXenRemove (xapiObjects, xapiIdsToXo, toRetry, conId) {
+    const conflicts = this._objectConflicts
+    const objects = this._xo._objects
+
+    forEach(xapiObjects, (_, xapiId) => {
+      toRetry && delete toRetry[xapiId]
+
+      const xoId = xapiIdsToXo[xapiId]
+      if (!xoId) {
+        // This object was not known previously.
+        return
+      }
+
+      delete xapiIdsToXo[xapiId]
+
+      const objConflicts = conflicts[xoId]
+      if (objConflicts) {
+        if (objConflicts[conId]) {
+          delete objConflicts[conId]
+        } else {
+          objects.set(xoId, popProperty(objConflicts))
+        }
+
+        if (isEmpty(objConflicts)) {
+          delete conflicts[xoId]
+        }
+      } else {
+        objects.unset(xoId)
+      }
+    })
+  }
+
+  async connectXenServer (id) {
+    const server = (await this._getXenServer(id)).properties
+
+    const xapi = this._xapis[server.id] = new Xapi({
+      url: server.host,
+      auth: {
+        user: server.username,
+        password: server.password
+      },
+      readOnly: Boolean(server.readOnly)
+    })
+
+    xapi.xo = (() => {
+      const conId = server.id
+
+      // Maps ids of XAPI objects to ids of XO objects.
+      const xapiIdsToXo = createRawObject()
+
+      // Map of XAPI objects which failed to be transformed to XO
+      // objects.
+      //
+      // At each `finish` there will be another attempt to transform
+      // until they succeed.
+      let toRetry
+      let toRetryNext = createRawObject()
+
+      const onAddOrUpdate = objects => {
+        this._onXenAdd(objects, xapiIdsToXo, toRetryNext, conId)
+      }
+      const onRemove = objects => {
+        this._onXenRemove(objects, xapiIdsToXo, toRetry, conId)
+      }
+      const onFinish = () => {
+        if (xapi.pool) {
+          this._xapis[xapi.pool.$id] = xapi
+        }
+
+        if (!isEmpty(toRetry)) {
+          onAddOrUpdate(toRetry)
+          toRetry = null
+        }
+
+        if (!isEmpty(toRetryNext)) {
+          toRetry = toRetryNext
+          toRetryNext = createRawObject()
+        }
+      }
+
+      const { objects } = xapi
+
+      const addObject = object => {
+        // TODO: optimize.
+        onAddOrUpdate({ [object.$id]: object })
+        return xapiObjectToXo(object)
+      }
+
+      return {
+        install () {
+          objects.on('add', onAddOrUpdate)
+          objects.on('update', onAddOrUpdate)
+          objects.on('remove', onRemove)
+          objects.on('finish', onFinish)
+
+          onAddOrUpdate(objects.all)
+        },
+        uninstall () {
+          objects.removeListener('add', onAddOrUpdate)
+          objects.removeListener('update', onAddOrUpdate)
+          objects.removeListener('remove', onRemove)
+          objects.removeListener('finish', onFinish)
+
+          onRemove(objects.all)
+        },
+
+        addObject,
+        getData: (id, key) => {
+          const value = xapi.getObject(id).other_config[`xo:${camelToSnakeCase(key)}`]
+          return value && JSON.parse(value)
+        },
+        setData: async (id, key, value) => {
+          await xapi._updateObjectMapProperty(
+            xapi.getObject(id),
+            'other_config',
+            { [`xo:${camelToSnakeCase(key)}`]: JSON.stringify(value) }
+          )
+
+          // Register the updated object.
+          addObject(await xapi._waitObject(id))
+        }
+      }
+    })()
+
+    xapi.xo.install()
+
+    try {
+      await xapi.connect()
+    } catch (error) {
+      if (error.code === 'SESSION_AUTHENTICATION_FAILED') {
+        throw new JsonRpcError('authentication failed')
+      }
+      if (error.code === 'EHOSTUNREACH') {
+        throw new JsonRpcError('host unreachable')
+      }
+      throw error
+    }
+  }
+
+  async disconnectXenServer (id) {
+    const xapi = this._xapis[id]
+    if (!xapi) {
+      throw new NoSuchXenServer(id)
+    }
+
+    delete this._xapis[id]
+    if (xapi.pool) {
+      delete this._xapis[xapi.pool.id]
+    }
+
+    xapi.xo.uninstall()
+    return xapi.disconnect()
+  }
+
+  // Returns the XAPI connection associated to an object.
+  getXapi (object, type) {
+    if (isString(object)) {
+      object = this.getObject(object, type)
+    }
+
+    const { $pool: poolId } = object
+    if (!poolId) {
+      throw new Error(`object ${object.id} does not belong to a pool`)
+    }
+
+    const xapi = this._xapis[poolId]
+    if (!xapi) {
+      throw new Error(`no connection found for object ${object.id}`)
+    }
+
+    return xapi
+  }
+
+  getXapiVmStats (vm, granularity) {
+    const xapi = this.getXapi(vm)
+    return this._stats.getVmPoints(xapi, vm._xapiId, granularity)
+  }
+
+  getXapiHostStats (host, granularity) {
+    const xapi = this.getXapi(host)
+    return this._stats.getHostPoints(xapi, host._xapiId, granularity)
+  }
+
+  async mergeXenPools (sourceId, targetId, force = false) {
+    const sourceXapi = this.getXapi(sourceId)
+    const {
+      _auth: { user, password },
+      _url: { hostname }
+    } = this.getXapi(targetId)
+
+    // We don't want the events of the source XAPI to interfere with
+    // the events of the new XAPI.
+    sourceXapi.xo.uninstall()
+
+    try {
+      await sourceXapi.joinPool(hostname, user, password, force)
+    } catch (e) {
+      sourceXapi.xo.install()
+
+      throw e
+    }
+
+    await this.unregisterXenServer(sourceId)
+  }
+}
diff --git a/src/xo.js b/src/xo.js
index 6b4536c25..0e4d7fd3d 100644
--- a/src/xo.js
+++ b/src/xo.js
@@ -10,29 +10,22 @@ import {EventEmitter} from 'events'
 import mixins from './xo-mixins'
 import Connection from './connection'
 import LevelDbLogger from './loggers/leveldb'
-import Xapi from './xapi'
-import xapiObjectToXo from './xapi-object-to-xo'
-import XapiStats from './xapi-stats'
 import {Acls} from './models/acl'
 import {
   mixin
 } from './decorators'
 import {
-  camelToSnakeCase,
   createRawObject,
   forEach,
   generateToken,
   isEmpty,
   mapToArray,
-  noop,
-  popProperty
+  noop
 } from './utils'
 import {
-  JsonRpcError,
   NoSuchObject
 } from './api-errors'
 import {ModelAlreadyExists} from './collection'
-import {Servers} from './models/server'
 import Token, {Tokens} from './models/token'
 
 // ===================================================================
@@ -43,12 +36,6 @@ class NoSuchAuthenticationToken extends NoSuchObject {
   }
 }
 
-class NoSuchXenServer extends NoSuchObject {
-  constructor (id) {
-    super(id, 'xen server')
-  }
-}
-
 // ===================================================================
 
 @mixin(mapToArray(mixins))
@@ -61,12 +48,6 @@ export default class Xo extends EventEmitter {
     this._objects = new XoCollection()
     this._objects.createIndex('byRef', new XoUniqueIndex('_xapiRef'))
 
-    // Connections to Xen servers.
-    this._xapis = createRawObject()
-
-    // Stats utils.
-    this._xapiStats = new XapiStats()
-
     // Connections to users.
     this._nextConId = 0
     this._connections = createRawObject()
@@ -74,7 +55,6 @@ export default class Xo extends EventEmitter {
     this._authenticationFailures = createRawObject()
     this._authenticationProviders = new Set()
     this._httpRequestWatchers = createRawObject()
-    this._xenObjConflicts = createRawObject() // TODO: clean when a server is disconnected.
 
     // Connects to Redis.
     this._redis = createRedisClient(config.redis && config.redis.uri)
@@ -97,11 +77,6 @@ export default class Xo extends EventEmitter {
       prefix: 'xo:acl',
       indexes: ['subject', 'object']
     })
-    this._servers = new Servers({
-      connection: redis,
-      prefix: 'xo:server',
-      indexes: ['host']
-    })
     this._tokens = new Tokens({
       connection: redis,
       prefix: 'xo:token',
@@ -110,21 +85,6 @@ export default class Xo extends EventEmitter {
 
     // ---------------------------------------------------------------
 
-    // Connects to existing servers.
-    const servers = await this._servers.get()
-    for (let server of servers) {
-      if (server.enabled) {
-        this.connectXenServer(server.id).catch(error => {
-          console.error(
-            `[WARN] ${server.host}:`,
-            error[0] || error.stack || error.code || error
-          )
-        })
-      }
-    }
-
-    // ---------------------------------------------------------------
-
     const handleStartError = error => {
       console.error(
         '[WARN] start error:',
@@ -149,8 +109,6 @@ export default class Xo extends EventEmitter {
   async stop () {
     this.stop = noop
 
-    // TODO: disconnect all servers.
-
     const handleStopError = error => {
       console.error(
         '[WARN] stop error:',
@@ -363,307 +321,6 @@ export default class Xo extends EventEmitter {
 
   // -----------------------------------------------------------------
 
-  async registerXenServer ({host, username, password, readOnly = false}) {
-    // FIXME: We are storing passwords which is bad!
-    //        Could we use tokens instead?
-    // TODO: use plain objects
-    const server = await this._servers.create({
-      host,
-      username,
-      password,
-      readOnly: readOnly ? 'true' : undefined,
-      enabled: 'true'
-    })
-
-    return server.properties
-  }
-
-  async unregisterXenServer (id) {
-    this.disconnectXenServer(id).catch(noop)
-
-    if (!await this._servers.remove(id)) { // eslint-disable-line space-before-keywords
-      throw new NoSuchXenServer(id)
-    }
-  }
-
-  async updateXenServer (id, {host, username, password, readOnly, enabled}) {
-    const server = await this._getXenServer(id)
-
-    if (host) server.set('host', host)
-    if (username) server.set('username', username)
-    if (password) server.set('password', password)
-
-    if (enabled !== undefined) {
-      server.set('enabled', enabled ? 'true' : undefined)
-    }
-
-    if (readOnly !== undefined) {
-      server.set('readOnly', readOnly ? 'true' : undefined)
-      const xapi = this._xapis[id]
-      if (xapi) {
-        xapi.readOnly = readOnly
-      }
-    }
-
-    await this._servers.update(server)
-  }
-
-  // TODO: this method will no longer be async when servers are
-  // integrated to the main collection.
-  async _getXenServer (id) {
-    const server = await this._servers.first(id)
-    if (!server) {
-      throw new NoSuchXenServer(id)
-    }
-
-    return server
-  }
-
-  _onXenAdd (xapiObjects, xapiIdsToXo, toRetry, conId) {
-    const conflicts = this._xenObjConflicts
-    const objects = this._objects
-
-    forEach(xapiObjects, (xapiObject, xapiId) => {
-      try {
-        const xoObject = xapiObjectToXo(xapiObject)
-        if (!xoObject) {
-          return
-        }
-
-        const xoId = xoObject.id
-        xapiIdsToXo[xapiId] = xoId
-
-        const previous = objects.get(xoId, undefined)
-        if (
-          previous &&
-          previous._xapiRef !== xapiObject.$ref
-        ) {
-          (
-            conflicts[xoId] ||
-            (conflicts[xoId] = createRawObject())
-          )[conId] = xoObject
-        } else {
-          objects.set(xoId, xoObject)
-        }
-      } catch (error) {
-        console.error('ERROR: xapiObjectToXo', error)
-
-        toRetry[xapiId] = xapiObject
-      }
-    })
-  }
-
-  _onXenRemove (xapiObjects, xapiIdsToXo, toRetry, conId) {
-    const conflicts = this._xenObjConflicts
-    const objects = this._objects
-
-    forEach(xapiObjects, (_, xapiId) => {
-      toRetry && delete toRetry[xapiId]
-
-      const xoId = xapiIdsToXo[xapiId]
-      if (!xoId) {
-        // This object was not known previously.
-        return
-      }
-
-      delete xapiIdsToXo[xapiId]
-
-      const objConflicts = conflicts[xoId]
-      if (objConflicts) {
-        if (objConflicts[conId]) {
-          delete objConflicts[conId]
-        } else {
-          objects.set(xoId, popProperty(objConflicts))
-        }
-
-        if (isEmpty(objConflicts)) {
-          delete conflicts[xoId]
-        }
-      } else {
-        objects.unset(xoId)
-      }
-    })
-  }
-
-  async connectXenServer (id) {
-    const server = (await this._getXenServer(id)).properties
-
-    const xapi = this._xapis[server.id] = new Xapi({
-      url: server.host,
-      auth: {
-        user: server.username,
-        password: server.password
-      },
-      readOnly: Boolean(server.readOnly)
-    })
-
-    xapi.xo = (() => {
-      const conId = server.id
-
-      // Maps ids of XAPI objects to ids of XO objects.
-      const xapiIdsToXo = createRawObject()
-
-      // Map of XAPI objects which failed to be transformed to XO
-      // objects.
-      //
-      // At each `finish` there will be another attempt to transform
-      // until they succeed.
-      let toRetry
-      let toRetryNext = createRawObject()
-
-      const onAddOrUpdate = objects => {
-        this._onXenAdd(objects, xapiIdsToXo, toRetryNext, conId)
-      }
-      const onRemove = objects => {
-        this._onXenRemove(objects, xapiIdsToXo, toRetry, conId)
-      }
-      const onFinish = () => {
-        if (xapi.pool) {
-          this._xapis[xapi.pool.$id] = xapi
-        }
-
-        if (!isEmpty(toRetry)) {
-          onAddOrUpdate(toRetry)
-          toRetry = null
-        }
-
-        if (!isEmpty(toRetryNext)) {
-          toRetry = toRetryNext
-          toRetryNext = createRawObject()
-        }
-      }
-
-      const { objects } = xapi
-
-      const addObject = object => {
-        // TODO: optimize.
-        onAddOrUpdate({ [object.$id]: object })
-        return xapiObjectToXo(object)
-      }
-
-      return {
-        install () {
-          objects.on('add', onAddOrUpdate)
-          objects.on('update', onAddOrUpdate)
-          objects.on('remove', onRemove)
-          objects.on('finish', onFinish)
-
-          onAddOrUpdate(objects.all)
-        },
-        uninstall () {
-          objects.removeListener('add', onAddOrUpdate)
-          objects.removeListener('update', onAddOrUpdate)
-          objects.removeListener('remove', onRemove)
-          objects.removeListener('finish', onFinish)
-
-          onRemove(objects.all)
-        },
-
-        addObject,
-        getData: (id, key) => {
-          const value = xapi.getObject(id).other_config[`xo:${camelToSnakeCase(key)}`]
-          return value && JSON.parse(value)
-        },
-        setData: async (id, key, value) => {
-          await xapi._updateObjectMapProperty(
-            xapi.getObject(id),
-            'other_config',
-            { [`xo:${camelToSnakeCase(key)}`]: JSON.stringify(value) }
-          )
-
-          // Register the updated object.
-          addObject(await xapi._waitObject(id))
-        }
-      }
-    })()
-
-    xapi.xo.install()
-
-    try {
-      await xapi.connect()
-    } catch (error) {
-      if (error.code === 'SESSION_AUTHENTICATION_FAILED') {
-        throw new JsonRpcError('authentication failed')
-      }
-      if (error.code === 'EHOSTUNREACH') {
-        throw new JsonRpcError('host unreachable')
-      }
-      throw error
-    }
-  }
-
-  async disconnectXenServer (id) {
-    const xapi = this._xapis[id]
-    if (!xapi) {
-      throw new NoSuchXenServer(id)
-    }
-
-    delete this._xapis[id]
-    if (xapi.pool) {
-      delete this._xapis[xapi.pool.id]
-    }
-
-    xapi.xo.uninstall()
-    return xapi.disconnect()
-  }
-
-  getXAPI () {
-    throw new Error(`Use <Xo#getXapi()> (camel case) instead.`)
-  }
-
-  // Returns the XAPI connection associated to an object.
-  getXapi (object, type) {
-    if (isString(object)) {
-      object = this.getObject(object, type)
-    }
-
-    const { $pool: poolId } = object
-    if (!poolId) {
-      throw new Error(`object ${object.id} does not belong to a pool`)
-    }
-
-    const xapi = this._xapis[poolId]
-    if (!xapi) {
-      throw new Error(`no connection found for object ${object.id}`)
-    }
-
-    return xapi
-  }
-
-  getXapiVmStats (vm, granularity) {
-    const xapi = this.getXapi(vm)
-    return this._xapiStats.getVmPoints(xapi, vm._xapiId, granularity)
-  }
-
-  getXapiHostStats (host, granularity) {
-    const xapi = this.getXapi(host)
-    return this._xapiStats.getHostPoints(xapi, host._xapiId, granularity)
-  }
-
-  async mergeXenPools (sourceId, targetId, force = false) {
-    const sourceXapi = this.getXapi(sourceId)
-    const {
-      _auth: { user, password },
-      _url: { hostname }
-    } = this.getXapi(targetId)
-
-    // We don't want the events of the source XAPI to interfere with
-    // the events of the new XAPI.
-    sourceXapi.xo.uninstall()
-
-    try {
-      await sourceXapi.joinPool(hostname, user, password, force)
-    } catch (e) {
-      sourceXapi.xo.install()
-
-      throw e
-    }
-
-    await this.unregisterXenServer(sourceId)
-  }
-
-  // -----------------------------------------------------------------
-
   // Returns an object from its key or UUID.
   //
   // TODO: should throw a NoSuchObject error on failure.