I found that we have currently separate tags for the different levels of raid : raid0, raid5, raid1. So, should they be merged into the main tag: raid, or do they provide necessary additional information?
They have different performance and redundancy characteristics.
Probably more importantly here, they have different steps to handle recoverable failures, different things to attempt recovery in a disaster, different steps required to to boot from them (e.g., RAID1 can boot w/o special bootloader support, RAID0, 4, 5, 6, can not). So, you often need to know the RAID level(s) involved to answer.
Personally, I view tags as largely about directing questions to the appropriate experts. I'm not sure if there are experts in a particular RAID level—so as a tag to follow, they fail.
However, others view tags as about categorization (and I personally think that's a good secondary use), and raid levels appear to be perfectly valid categorization. Also useful, I suppose if you're searching for a question about booting from RAID5.
In my opinion (as a storage engineer, so appreciate my perspective might differ from most of U&L):
RAID variant is a configuration detail. If you are here asking a question about RAID, then there are other configuration details more important than the RAID mode. Like hardware platform, OS, controller type, HBA model, disk tech.
These are usually more significant details in filtering a question about RAID, and as such I would suggest they would be worth synonym-ising to
Having built RAID 0, 1, 5, 6, and just recently RAID-10 arrays in Kali Linux, I found the differences in each class to be very interesting. My usb is needed of course to boot up my RAID-10, and two of the RAID arrays I built inside the usb, which incidentally is 65 Gigs. The difference in performance in my system now is indeed noteworthy after going from RAID-6 to RAID-10. I'm the new guy here, and it looks like I've already pissed someone off, oops. Anyways, I don't see any harm in having separate, specific tags for each structure.