What is the best RAID to do on a 4-disk NAS for the home?

Question

NAS

I plan to buy a NAS for home with a total capacity of 30 terabytes. For backups of family members' computers, music collection, file storage. Most likely Synology. They seem to work well with Mac for backups. Disks plan WD RED 8-10-12 TB. In order to have at least some reliability, there is a RAID5 option: 4 disks of 10 TB each will give 3 * 10 = 30 TB. It seems to be not bad, you can buy disks for 12 TB, there the difference is already small. Question: Is RAID5 optimal for such a task? Can I take a NAS not for 4, but for 6 disks and glue another RAID? I've just always worked only with mdadm raid1 :) no practice with problems of 4-6 disks in the array.
Total:
1. what variant of nas for the home should be taken for a total capacity of 30 TB, so that when at least one of any disk comes out, everything does not crash in an instant?
2. in my opinion, there is a high probability of failure of not one, but two disks at once (they are bought at the same time, even if I buy from different suppliers, there may be one production batch). Which RAID option to take in order not to be afraid of the collapse of 2 disks in the array?

Answer 1

Question: Is RAID5 optimal for such a task?

Yes.
NAS or RAID? If NAS, then you correctly chose Synology, if RAID, then 5.
No, the probability of this option is orders of magnitude lower than the failure of one.
RAID 6. But you "five" for the eyes.
After all, this is a backup server.

Answer 2

raid5 is the ability to safely lose one disk
raid6 is the ability to lose two disks
An example of why it would make sense to use raid 6 - when one disk dies, you buy a replacement for it and the whole raid starts the rebuild operation, this is a very long operation, it works in idle , i.e. should not noticeably slow down the entire array, but can last for days. Unfortunately, due to the increased load on the disks, all those jambs that led that dead disk to death can also appear on the remaining disks (this is especially true for disks of the same manufacturer and one batch), i.e. the chances of disks dying at the time of the array rebuild are higher, and raid6 will monitor the reliability of data during this period.
ps It is recommended to take the same disks so that they have the same timings, this is especially true for hardware raids, literally a quote, you can get a ruined raid from scratch because of this.
I suppose this is true for hardware raids focused on performance, and home soft raids do not suffer from this problem.

Answer 3

RAID5 is optimal for this task

Not
Keyword - glue another RAID
raid6 and variations.

Answer 4

Here you still have to think that if the piece of iron dies, it was possible to reproduce this RAID on another piece of hardware.
Which is not always obvious and can be done.
In my opinion, the simpler the better - a mirror.