Is it worth changing the current Raid?

Question

RAID

I have two hard drives in raid1. if I add a new disk and change raid1 to raid5 will I lose data in old disks or not?

Answer 1

It looks like there are 2 questions.
1. on the topic in the question - Yes, it is, thus the failure resistance is higher and the performance in this case will not be lost.
2. Yes, you can lose data, but you don't have to.
I suggest, of course, if your platform RAID controller (because nothing is said) can use an additional disk as a hot-spare. unless of course the goal is to increase the partition space, and not lose data.

Answer 2

I have a NAS. I am using 2 wd red 4tb RAID1. I wanted to buy additional 4tb and change to RAID5. As I understand it, I will lose it or make an additional RAID.

Answer 3

Of course you will lose. RAID 1 and RAID 5 are two different ways to distribute data across disks.
You need to copy the data somewhere else, add a disk, create RAID5 from all disks and then copy the data back to it.
I have come across proprietary utilities from manufacturers that seem to allow you to change the array type on the fly, for example, from RAID5 to RAID6, but I would not recommend using anything like that. If something goes wrong in the process, data recovery will be difficult and expensive.