"If you're even doing them at all." - Me
"Raid is not a backup" - Me
I had to go to a client for a multiple hard drive failure. Not a pleasant visit. He had 2 NAS with 2 RAID1 arrays. 3 disk failed at the same time. the 4th turned out to bricked too. It showed that the data was there, but the lookup table was gone.
I tried everything: From my MacBook, from another Mac, I even tried to boot from a Linux USB stick to see if there was something I could do that the Mac couldn't. Nothing.
They lost 20 years of company data. When you need to give that kind of news it's devastating.
Think about backups before you have an issue
1. Don't use RAID as a backup
Even if RAID 1 does a 1:1 copy and that seems enough to most people, it's still not a backup.
- If a file gets corrupted on one drive, it'll be corrupted on the second drive too
- If you need an older version of a file you're out of luck
- If there is a power surge both drives will be toast
2. Have an offsite backup
The probable cause of all of this was some power spike. It seems unlikely to me that all 4 drives failed at the same time even though it surely is possible, especially since they were all bought around the same time and used for the same amount of time and for the same task.
Not really backups but if you don't have a lot of data to back up you can use:
- Google Drive
- iCloud Drive
3. Have multiple backup strategies
Only one backup is not enough if your data is valuable. Consider having more than one backup strategy. One on site. One off-site. At least.