Firstly to answer your questions:
so my first question is can i make another partition separate from my
data partition on the same hard drive and use that as windows
partition without losing any data ?
Yes, you can make another partition, but it is rather complicated and risky. You can use tools like "GParted" or similar to resize a partition on your external drive and create a new partition in the freed space. You cannot use GParted from the Ubuntu installation, because the system partition would be blocked. You need to boot GParted live from USB or CD. However, I strongly recommend NOT doing this if you cannot afford losing the entire data, due to the following reasons:
- Power failure or hardware error might prevent the process from completing.
- The tools might have bugs.
- You might accidentally select and format the wrong partition and lose the data.
If the process is interrupted your data might be lost, or you might need a very time consuming procedure to recover the data.
In case your data is not that important and you can afford to lose it, then maybe you can try to resize the partitions.
I am not 100% confident about that but my impression is that there is sometimes a difference between a GParted formatted partition and a Windows formatted one, even if you use the same NTFS format. In order to avoid errors, I prefer formatting with Windows itself and formatting the whole drive from scratch (no resizing).
secondly what are the chances that my data gets lost at some
point(consider that i have no backup of my data and the data is much
more crucial then having windows) ?
In this case I strongly discourage you from meddling with the external drive's partitions. In your shoes I would also create a second copy of this data - you never know, disks go defective sometimes (10 years on paper, but I would not take chances).
And now some ideas:
- You can buy a USB pen drive with USB 3.0 and 64 or even 128 GB and install windows on it. Should cost about 20-30 $ online.
- Buying a second external drive and copying your data would be also a good idea, if you can afford it. I always keep at least 4 identical copies of all my files in different locations.
- If you have a laptop with a HDD/DVD Caddy like this one for Lenovo - check your compatibility first (my favorite option), then you can remove the DVD drive and buy a caddy with a 2.5" internal HDD, on which you could install Windows. For the installation itself you need to attach it internally - you need of course both DVD and the HDD. But after the installation it can be in the caddy.
- If you don't mind, you can install Windows in a virtual machine in your Ubuntu. This would store the data in a file. You can use software like QEMU (raw or with libvirt and virt-manager) or VirtualBox, VMWare, ...
I wish you good luck.