diff --git a/docs/manuals/en/new_main_reference/source/conf.py b/docs/manuals/en/new_main_reference/source/conf.py
index 2b64da7e2cd..4c0c794083b 100644
--- a/docs/manuals/en/new_main_reference/source/conf.py
+++ b/docs/manuals/en/new_main_reference/source/conf.py
@@ -245,3 +245,5 @@
 
 #scv_root_ref = 'dev/pstorz/bareos-18.2/sphinx-versioning'
 #scv_banner_main_ref = 'dev/pstorz/bareos-18.2/sphinx-versioning'
+
+plantuml_output_format = 'svg_img'
diff --git a/docs/manuals/en/new_main_reference/source/developers.rst b/docs/manuals/en/new_main_reference/source/developers.rst
index fd0c7565741..2641d54bc68 100644
--- a/docs/manuals/en/new_main_reference/source/developers.rst
+++ b/docs/manuals/en/new_main_reference/source/developers.rst
@@ -21,3 +21,4 @@ Bareos Developer Guide
    developers/netprotocol.rst
    developers/directorConsole.rst
    developers/smartall.rst
+   developers/reservation.rst
diff --git a/docs/manuals/en/new_main_reference/source/developers/reservation.rst b/docs/manuals/en/new_main_reference/source/developers/reservation.rst
new file mode 100644
index 00000000000..f87e5c6cd7c
--- /dev/null
+++ b/docs/manuals/en/new_main_reference/source/developers/reservation.rst
@@ -0,0 +1,35 @@
+Reservation
+===========
+
+Introduction
+------------
+After the director set up a job on the SD it will then issue a "use" command to tell the SD what storage device it wants to use.
+The SD then checks the list of devices the director sent and tries to reserve a suitable device.
+In the end the SD either tells the director which device to use or that there is no device available for the job.
+
+There is a so-called reservation context that is passed to every function that has a swimlane in this diagram.
+This context is basically a bunch of flags that are set and cleared to change the behaviour of the rest of the code.
+
+For example CanReserveDevice() from the second diagram sets the flag low_use_drive which is then evaluated in UseDeviceCmd().
+
+Diagram Conventions
+~~~~~~~~~~~~~~~~~~~
+Each swimlane denotes a separate function.
+
+.. include:: reservation/legend.puml
+
+UseDeviceCmd
+~~~~~~~~~~~~
+This function reads the list of storages and devices the director is willing to use for this job.
+Afterwards several different methods of finding a device to reseve are used.
+If no device could be reserved the function waits for up to a minute or until ReleaseDeviceCond() is called and then tries again.
+
+.. include:: reservation/UseDeviceCmd.puml
+
+ReserveDevice
+~~~~~~~~~~~~~
+Here we see wether the media type matches and actually try to open the device.
+The actual reservation is delegated to ReserveDeviceForRead() or ReserveDeviceForAppend().
+While the first one is more or less trivial, the latter one is really complicated.
+
+.. include:: reservation/ReserveDevice.puml
diff --git a/docs/manuals/en/new_main_reference/source/developers/reservation/ReserveDevice.puml b/docs/manuals/en/new_main_reference/source/developers/reservation/ReserveDevice.puml
new file mode 100644
index 00000000000..713ec4d72c0
--- /dev/null
+++ b/docs/manuals/en/new_main_reference/source/developers/reservation/ReserveDevice.puml
@@ -0,0 +1,154 @@
+.. uml::
+  :caption: Control flow of ReserveDevice()
+
+  @startuml
+  |ReserveDevice|
+  start
+  #limegreen:if (device matches requested media_type?) then (yes)
+    if (device initialized?) then (no)
+      :InitDev()|
+    endif
+    if (device exists and is open?) then (yes)
+      #aqua:set suitable_device]
+      :initialize DCR;
+      if (append?) then (no)
+        :ReserveDeviceForRead()|
+      else (yes)
+        |ReserveDeviceForAppend|
+        if (CanRead()) then (no)
+          if (IsDeviceUnmounted()) then (no)
+            |CanReserveDrive|
+            if (IsMaxJobsOk()) then (yes)
+              #aqua:if (any_drive set?) then (no)
+                #aqua:if (try_low_use_drive set?) then (yes)
+                  #aqua:if (low_use_drive is current drive?) then (yes)
+                    (S)
+                    detach
+                  endif
+                endif
+                #aqua:if (PreferMountedVols set?) then (no)
+                  if (isBusy()) then (yes)
+                    #aqua:if (dev.num_writers + NumReserved() < num_writers) then (yes)
+                      #aqua:set num_writers := dev.numwriters + NumReserved()]
+                      #aqua:set low_use_drive := dev]
+                    endif
+                    (X)
+                    detach
+                  endif
+                else (yes)
+                  if (IsTape() but no volume) then (yes)
+                    (X)
+                    detach
+                  endif
+                endif
+                #aqua:if(exact_match set? and have_volume set?) then (yes)
+                  #aqua:if(VolumeName matches mounted volume) then (no)
+                    (X)
+                    detach
+                  endif
+                  if (Can_i_use_volume()) then (no)
+                    (X)
+                    detach
+                  endif
+                endif
+                :line 1080;
+
+                :line 1152;
+              endif
+              #aqua:if (autochanger_only) then (yes)
+                if (IsBusy()) then (no)
+                  if (volume in drive) then (no)
+                    (S)
+                    detach
+                  endif
+                endif
+              endif
+              if (num_writers == 0) then (yes)
+                if (NumReserved()) then (yes)
+                  if (IsPoolOk()) then (yes)
+                    (S)
+                    detach
+                  else (no)
+                    (X)
+                    detach
+                  endif
+                elseif (CanAppend()) then (yes)
+                  if (IsPoolOk()) then (no)
+                    :UnloadAutoChanger()|
+                  endif
+                  (S)
+                  detach
+                endif
+              endif
+              if (num_writers > 0 || CanAppend()) then (yes)
+                if (IsPoolOk()) then (yes)
+                  (S)
+                  #tomato:return success;
+                else (no)
+                  (X)
+                  detach
+                endif
+              else (no)
+                #tomato:cancel job (M_FATAL);
+                detach
+              endif
+            else (no)
+              (X)
+              #tomato:return failure;
+            endif
+            |ReserveDeviceForAppend|
+            if (success?) then (yes)
+              :reserve device;
+              :set have_device]
+            endif
+          endif
+        endif
+        |ReserveDevice|
+        if (have_device?) then (yes)
+          #aqua:if (have_volume set?) then (yes)
+            if (reserve_volume()) then (no)
+              (F)
+              detach
+            endif
+          else (no)
+            if (DirFindNextAppendableVolume()) then (yes)
+              #aqua:set have_volume]
+              #aqua:set VolumeName]
+            else (no)
+              #aqua:clear have_volume]
+              #aqua:clear VolumeName]
+              if (FoundInUse()) then (yes)
+                #aqua:if(PreferMountedVols set?) then (no)
+                  #aqua:set PreferMountedVols]
+                  if (dcr has volume?) then (yes)
+                    :UnreserveDevice()|
+                  endif
+                  (F)
+                  detach
+                endif
+              endif
+              if (num_writers != 0) then (yes)
+                  if (dcr has volume?) then (yes)
+                    :UnreserveDevice()|
+                  endif
+                  (F)
+                  detach
+              endif
+            endif
+          endif
+        else (no)
+          (F)
+          detach
+        endif
+      endif
+  if (have_device?) then (yes)
+    :OK device message>
+  else (no)
+    (F)
+    #aqua:clear have_volume]
+    #aqua:clear VolumeName]
+  endif
+    endif
+  endif
+
+  @enduml
diff --git a/docs/manuals/en/new_main_reference/source/developers/reservation/UseDeviceCmd.puml b/docs/manuals/en/new_main_reference/source/developers/reservation/UseDeviceCmd.puml
new file mode 100644
index 00000000000..3c288403202
--- /dev/null
+++ b/docs/manuals/en/new_main_reference/source/developers/reservation/UseDeviceCmd.puml
@@ -0,0 +1,191 @@
+.. uml::
+  :caption: Control flow of UseDeviceCmd()
+
+  @startuml
+  'BEGIN macros
+  !definelong RESERVE_DEVICE()
+  :ReserveDevice()|
+  !enddefinelong
+
+  !definelong AUTOCHANGER()
+  partition autochanger {
+    while (with each device in autochanger device)
+      #limegreen:if (device autoselect?) then (yes)
+        RESERVE_DEVICE()
+        if (have_device?) then (yes)
+          #tomato:return;
+          detach
+        endif
+      endif
+    endwhile
+  }
+  !enddefinelong
+
+  !definelong PLAIN_DEVICE()
+  partition plain_device {
+  RESERVE_DEVICE()
+  note right
+    try to reserve the named device
+  end note
+  if (have_device?) then (yes)
+    #tomato:return;
+    detach
+  endif
+  #limegreen:if (DeviceReserveByMediatype) then(yes)
+    while (each device with matching media_type)
+      RESERVE_DEVICE()
+      if (have_device?) then (yes)
+        #tomato:return;
+        detach
+      endif
+    endwhile
+  endif
+  }
+  !enddefinelong
+
+  !definelong MOUNTED_VOLUMES()
+  partition mounted_volumes {
+  if (append?) then(yes)
+    while(with each mounted volume)
+      :ask director if volume is ok/
+      if (volume ok?) then(yes)
+        :find device for volume;
+        RESERVE_DEVICE()
+        if (have_device?) then (yes)
+          #tomato:return;
+          detach
+        endif
+      endif
+    endwhile
+  endif
+  }
+  !enddefinelong
+  'END macros
+  |UseDeviceCmd|
+  start
+  partition read_data_from_director {
+    repeat
+      :storage specification<
+      repeat
+        :device specification<
+      repeat while (more devices?)
+    repeat while (more storages?)
+  }
+
+    repeat
+    #aqua:clear suitable_device]
+    #aqua:clear have_volume]
+    #aqua:clear VolumeName]
+    #aqua:clear any_drive]
+    #limegreen:if (PreferMountedVols) then (no)
+        #aqua:clear low_use_drive]
+        #aqua:clear PreferMountedVols]
+        #aqua:clear exact_match]
+        #aqua:set autochanger_only]
+        |FindSuitableDeviceForJob|
+        while (with every device)
+          |SearchResForDevice|
+          AUTOCHANGER()
+          |FindSuitableDeviceForJob|
+        endwhile
+        |UseDeviceCmd|
+        if (have_device) then (yes)
+          stop
+        else (no)
+          #aqua:if (low_use_drive set?) then (yes)
+            #aqua:set try_low_use_drive]
+            |FindSuitableDeviceForJob|
+            while (with every device)
+              |SearchResForDevice|
+              AUTOCHANGER()
+              |FindSuitableDeviceForJob|
+            endwhile
+            |UseDeviceCmd|
+            if (have_device) then (yes)
+              stop
+            endif
+            #aqua:clear try_low_use_drive]
+          endif
+          #aqua:clear autochanger_only]
+          |FindSuitableDeviceForJob|
+          while (with every device)
+            |SearchResForDevice|
+            AUTOCHANGER()
+            PLAIN_DEVICE()
+            |FindSuitableDeviceForJob|
+          endwhile
+          |UseDeviceCmd|
+          if (have_device) then (yes)
+            stop
+          endif
+        endif 
+      else (yes)
+      endif  
+      #aqua:set PreferMountedVols]
+      #aqua:set exact_match]
+      #aqua:clear autochanger_only]
+      |FindSuitableDeviceForJob|
+      MOUNTED_VOLUMES()
+          while (with every device)
+            |SearchResForDevice|
+            AUTOCHANGER()
+            PLAIN_DEVICE()
+            |FindSuitableDeviceForJob|
+          endwhile
+      |UseDeviceCmd|
+      if (have_device) then (yes)
+        stop
+      else (no)
+        #aqua:clear exact_match]
+        |FindSuitableDeviceForJob|
+      MOUNTED_VOLUMES()
+          while (with every device)
+            |SearchResForDevice|
+            AUTOCHANGER()
+            PLAIN_DEVICE()
+            |FindSuitableDeviceForJob|
+          endwhile
+        |UseDeviceCmd|
+        if (have_device) then (yes)
+          stop
+        else (no)
+          #aqua:set any_drive]
+          |FindSuitableDeviceForJob|
+      MOUNTED_VOLUMES()
+          while (with every device)
+            |SearchResForDevice|
+            AUTOCHANGER()
+            PLAIN_DEVICE()
+            |FindSuitableDeviceForJob|
+          endwhile
+          |UseDeviceCmd|
+          if (have_device) then (yes)
+            stop
+          else (no)
+            if (attempt 3+?) then (yes)
+              :wait 30 seconds;
+            else (no)
+              #aqua:if (suitable_device set?) then (yes)
+                :WaitForDevice()|
+                note right
+                  This will acquire a mutex to queue up
+                  multiple jobs waiting for a device.
+                  Then it waits up to 60 seconds for some
+                  other thread to call ReleaseDeviceCond()
+                end note
+              else (no)
+                (F)
+                detach
+              endif
+            endif
+          endif
+        endif
+      endif
+    repeat while (repeat forever)
+    detach
+  partition failed_to_reserve {
+    (F)
+    :no device message>
+    stop
+  }
+  @enduml
diff --git a/docs/manuals/en/new_main_reference/source/developers/reservation/legend.puml b/docs/manuals/en/new_main_reference/source/developers/reservation/legend.puml
new file mode 100644
index 00000000000..6b7d015dd99
--- /dev/null
+++ b/docs/manuals/en/new_main_reference/source/developers/reservation/legend.puml
@@ -0,0 +1,24 @@
+.. uml::
+  :caption: Diagram legend
+  
+  @startuml
+  #aqua:reservation context is read or set;
+  detach
+  #limegreen:Decision based on configuration directive;
+  detach
+  #tomato:Control flow broken;
+  detach
+  (M)
+  note right
+    goto or jump-mark
+  end note
+  detach
+  :Read read data from the network<
+  detach
+  :Send data to the network>
+  detach
+  :Call another function|
+  detach
+  :Remote procedure call/
+
+  @enduml