I have a main disk named /dev/vda1 and this is the storage properties:

ubuntu@demo:~$ df -h

Filesystem      Size  Used Avail Use% Mounted on

udev             16G     0   16G   0% /dev

tmpfs           3.2G  8.8M  3.2G   1% /run

/dev/vda1        39G   37G  2.7G  94% /

tmpfs            16G  4.0K   16G   1% /dev/shm

tmpfs           5.0M     0  5.0M   0% /run/lock

tmpfs            16G     0   16G   0% /sys/fs/cgroup

tmpfs           3.2G     0  3.2G   0% /run/user/1000

as you see it has some free space. When I run the fdisk command there is some other partitions:

ubuntu@demo:~$ sudo fdisk -l

Disk /dev/vda: 40 GiB, 42949672960 bytes, 83886080 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: dos

Disk identifier: 0xdcd70aad



Device     Boot Start      End  Sectors Size Id Type

/dev/vda1  *     2048 83886046 83883999  40G 83 Linux





Disk /dev/vdb: 15 GiB, 16106127360 bytes, 31457280 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes





Disk /dev/vdc: 20 GiB, 21474836480 bytes, 41943040 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

It seems I have some other partitions which I am not using. How I can merge these partitions with my main storage (/dev/vda1)?
I am using 16.04 version and it is a server version.

No it can't be done

First, let us be clear about some terminology. memory is RAM what we are discussing here is storage in the form of virtual disks. RAM is not mounted or partitioned, on the other hand storage as a physical (or a virtual) drive can be partitioned and then mounted.

The fdisk command shows your virtual Ubuntu server has three virtual drives, not three unmounted partitions in a single virtual drive. If you had a physical computer with three physical disk drives, you wouldn't be able to smash them together and make a single physical drive. Similarly, you won't be able merge these virtual drives into a single drive.

There is a way to do this using Logical Volume Manager (LVM), but that would require erasing everything in in /dev/vda/ and do it at the time of a new install.

There is another way

Since your drives are not physical, but virtual you should be able to increase the size of /dev/vda when the virtual server is turned off using some tools in the virtualization software in the host computer. The exact method will depend on the host operating system (Ubuntu, Windows, etc.) and the specific virtualization software you are using (qemu, Virtual Box, VMWare etc.).

If you are not using /dev/vdb and /dev/vdc you may delete these from the virtualization software and the corresponding files host computer.

Hope this helps