RAID 10 is the spanning of two or more RAID 1 mirrors. In this case, it tolerates a single drive failure for each spanned volume. However, the array would be offline if both of the drives from the same span fail.
On the image below, you can lose a drive for each RAID 1 and be able to boot to your Operating System. If you lose both drives from the same RAID 1 you won’t be able to boot to your Operating System.
You can always find useful information about our RAID solutions here.