Please someone help me.
I’m working in a company that already had a hardware raid 5 storage but they are looking for better solutions to storage sensitive data. I think TrueNAS gonna be a good solution but need to know more in depth about. Considering we have a lot of data to be storage that cannot be lost.
Firstly, where are located the operating system of TrueNAS inside the computer?
And, I feel that I’m not confident yet, to explain about ZFS because I know only the surface of it.
If someone can explain more about it I’ll be grateful. 
How it works technically speaking?
The operating system is located on whatever device you install it onto. Typically this should be a small-ish SSD, or perhaps a mirrored pair of them.
For mission critical storage in a company setting and especially for securing sensitive data, I would recommend starting here:
Do you think use the free features available for this “mission” isn’t a good idea?
I think if you’re relying on a system for your business, you need solid support available. Yes, it’s going to cost–though perhaps less than you think. But I think it’d be unwise to wing it here.
-
TrueNAS SCALE is built on ZFS and with both you can manage very large RAIDZ (like RAID 5/6) storage with hundreds of disks.
-
You will need Enterprise support from iXsystems, and you will need to choose hardware carefully (either 3rd party hardware supported by iX or iXsystems own TrueNAS hardware). But even with Enterprise support, this will cost substantially less than e.g. a specialised EMC disk array.
-
You need expert support in designing your disk layouts. Don’t skimp on this because any mistakes here will be difficult and costly to rectify later and if you have an irrecoverable loss of data later you will regret any design flaws that contributed to it.