once in a while after a reboot I found fsck would fail on OS disk and
booting becoming impossible on many of my servers.
Are you doing graceful reboots/shutdowns on these systems? If you are doing so (meaning filesystems get cleanly un-mounted), and you are still seeing corruption, then it's likely that the underlying storage has issues.
What filesystem are you using? Hopefully you're using a journaled filesystem? With journaled filesystems, even if they go down hard (meaning the server gets shut down before a clean un-mount), large-scale corruption is very un-likely.
1.regular scheduled fsck on disks
Doing so won't hurt, but it's also not all that necessary if your hardware is good.
- use raid 5/6
RAID won't do a thing for you. RAID protects from hardware failure, not filesystem failure.