diff --git a/admindoc.md b/admindoc.md
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--- a/admindoc.md
+++ b/admindoc.md
@@ -30,6 +30,7 @@
     * [Backup](/backup)
 * Going further
     * [Improving security](/security)
+    * [Adding an external storage](/external_storage)
     * [Migrating emails to YunoHost](/email_migration)
     * [Hide services with Tor](/torhiddenservice)
 * [Troubleshooting guide](/troubleshooting_guide)
diff --git a/external_storage.md b/external_storage.md
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+# Adding an external storage to your server
+
+## Introduction
+
+If you did not allocate a large partition to `/home` before installing YunoHost, and that your apps require a lot of spaces, you can still add an external driver after setting up your system.
+
+## Before starting
+
+Even though these steps are relatively simple, they may appear technical. In any case, they require you to **take your time**.
+
+You should be connected as root on your server, for instance via [SSH](/ssh). (Note: being logged as `admin`, you can upgrade to `root` with the command `sudo su`)
+
+It can be useful to [create a backup](/backup) of your install before starting.
+
+You should also have your external drive (plugged via USB or SATA).
+
+## 1. Connect and identify the disk
+
+Start by connecting your drive to the system. You shall then identify which name is used by the system to refer to the disk.
+
+You can do this with this command :
+
+```bash
+lsblk
+```
+
+It may yield something like this :
+
+```bash
+NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
+sda           8:0    0 931.5G  0 disk 
+└─sda1        8:1    0 931.5G  0 part 
+mmcblk0     179:0    0  14.9G  0 disk 
+├─mmcblk0p1 179:1    0  47.7M  0 part /boot
+└─mmcblk0p2 179:2    0  14.8G  0 part /
+```
+
+Here, `mmcblk0` corresponds to an SD card of 16Go (the partitions `mmcblk0p1` et `mmcblk0p2` are used as the boot partition `/boot` and the system partition `/`). The external drive is `sda` which is about 1TB and has only one partition `sda1` which is not mounted (no "MOUNTPOINT").
+
+<div class="alert alert-warning" markdown="1">
+<span class="glyphicon glyphicon-warning-sign"></span> On a different setup, your system partition might be `sda` and so your external drive might be `sdb` for instance.
+</div>
+
+## 2. (Optionnal) Format the disk
+
+If you want, you can format the disk before starting to use it. You should be aware that **formating a drive implies to erasing every data on it !** If your disk is already "clean", you may ignore this step.
+
+To format the partition :
+
+```bash
+mkfs.ext4 /dev/YOUR_DISK
+# then 'y' to validate
+```
+
+(Replace `YOUR_DISK` by the name of the disk. Be careful not to do any mistake here, as it can mean erasing data on your main system if you are using the wrong name ! In the previous example, the name of our disk was `sda`.)
+
+Then, let's create a new partition on the disk which just got formatted :
+
+```bash
+fdisk /dev/YOUR_DISK
+```
+
+then sucessfully type `n`, `p`, `1`, `Enter`, `Enter`, then `w` to create the new partition.
+
+Check with `lsblk` that your disk really does contain a single partition.
+
+## 3. Mount the disk
+
+"Mounting" a disk corresponds to making it effectively accessible in the filesystem tree. Here, we choose the arbitrary name `/media/storage` but you can choose a different name (for instance, `/media/my_disk` ... ).
+
+Let's start by creating the directory :
+
+```bash
+mkdir /media/storage
+```
+
+Then we can manually mount the disk with :
+
+```bash
+mount /dev/YOUR_DISK /media/storage
+```
+
+Next, you should be able to create files in `/media/stockage`, and, for instance, add `/media/stockage` as an external drive in Nextcloud.
+
+## 4. Mount the disk automatically at boot
+
+So far, we only mounted the disk manually. But it can be nice and useful to have it being mounted automatically at each boot.
+
+Let's start by finding the UUID (universal identifier) of the disk with :
+
+```bash
+blkid | grep "/dev/YOUR_DISK:"
+# Should return something like
+# /dev/sda:UUID="cea0b7ae-2fbc-4f01-8884-3cb5884c8bb7" TYPE="ext4" PARTUUID="34e4b02c-02"
+```
+
+Let's add a line in the file `/etc/fstab` which manages which disks are mounted at boot. We open this file with `nano` :
+ 
+```bash
+nano /etc/fstab
+```
+
+And add this line :
+
+```bash
+UUID="cea0b7ae-2fbc-4f01-8884-3cb5884c8bb7" /media/storage ext4 defaults,nofail 0 0
+```
+
+(this line should be adapated according to previous info and choices)
+
+Use Ctrl+X then `y` to save.
+
+You can then reboot the system to test if the disk is mounted automatically.
+