Update cookbook.md

pages/cookbook.md

@@ -10,6 +10,8 @@
 ```
 
 ## Upload .ISO images manually
+Specifically to v2.
+
 1. Remount internal storage to rw (read-write):
     ```
     # kvmd-helper-otgmsd-remount rw
@@ -69,3 +71,56 @@ Specifically to v2. When combined with configuring a DNS server, FTP, or SMB (fo
 2. Perform `reboot`.
 
 :exclamation: When this feature is activated, the Pi-KVM interface and other ports will be available to the host. Use iptables for restrictions.
+
+## Adding extra Mass Storage Drives
+Specifically to v2. By default, Pi-KVM creates only one drive for Mass Storage emulation. However, you can create additional drives and manage them manually via the terminal. This is useful if you want to boot the server from a ISO CD (specified in the web interface), then connect a virtual flash drive to the server and download some files from to Pi-KVM from it.
+
+:exclamation: The presence of an additional Mass Storage device should not interfere with the download, but for reasons of compatibility paranoia, this is disabled by default. We recommend setting up the drives in advance, making sure that booting from the ISO CD is still working, and then using the drives as needed.
+
+How to enable extra drives:
+1. Switch the root filesystem to `rw` mode.
+2. Edit `/etc/kvmd/override.yaml` (remove `{}` if this your first configuration entry) and add these lines:
+    ``` yaml
+    otg:
+        devices:
+            drives:
+                enabled: true  # Set it to true to enable
+                count: 1  # +1 drive, default value
+                default:  # Default configuration for the all extra drives
+                    cdrom: false  # Defaut value (false for the generic flash drive)
+                    rw: false # Read-only by default
+    ```
+    If you specify `count: N`, you will create `N` additional drives configured the same way, as described in the `default` section.
+3. Reboot.
+
+How to create RW flash drive:
+1. Switch the root filesystem to `rw` mode:
+    ```
+    # rw
+    ```
+2. Create the empty image file of the desire size (1Gb in this example.
+    ```
+    # dd if=/dev/zero of=/root/flash.img bs=1024
+    ```
+3. Connect it to the drive 1:
+    ```
+    # kvmd-otgmsd -i 1 --set-rw=1 --set-cdrom=0 --set-image=/root/flash.img
+    ```
+    After that you will have access to the flash drive from the server.  
+    :exlcamation: Drive 0 represents a drive that is controlled via a web interface and API. Don't use it with kvmd-otgmsd if you don't know exactly what you're doing.
+4. View the driver state:
+    ```
+    # kvmd-otgmsd -i 1
+    Image file:  /root/flash.img
+    CD-ROM flag: no
+    RW flag:     yes
+5. To disable the flash drive and view the files on it from the KVM, run:
+    ```
+    # kvmd-otgmsd -i 1 --unlock --eject
+    ```
+    :exclamation: this command will interrupt the current IO operation on **ALL DRIVES** including the one that is managed via the web interface. The same result is achieved by clicking the disable media button in the web interface. Right now, the Linux kernel does not allow to distinguish between internal threads that manage different drives. It is recommended to eject the media when you know that this will not cause problems for the other media.
+6. Don't forget to remount the root filesystem to read-only mode:
+    ```
+    # ro
+    ```
+7. You can download the resulting image via SCP or mount it as a loop device on the Pi-KVM.