Perhaps repeating myself, but consider no-RAID or RAID "0" and -M MaxMetadataReplicas Specifies the default maximum number of copies of inodes, directories, and indirect blocks for a file. Valid values are 1, 2, and 3. This value cannot be less than the value of DefaultMetadataReplicas. The default is 2.
SO you can have triple redundancy with no shared physical point of failure. When you depend a particular RAID controller to do replication and subsequent recovery for you, then you are depending on that RAID controller. Of course, when you take this point of view to the extreme, you realize that for any individual datum you are depending on the single generator or source of that datum being correct, the OS and filesystem software and CPU, etc, etc.... Until you get to the point just beyond where the datum is replicated...
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