Well he is going against what many IT professionals would recommend. Having 20TB drives that is. Having more smaller drives as in the use case that just happened making this one be necessary to be a thing. Now think what would have happened if instead of just 16TB drives there was 20TB drives that had 2 of them fail with data? Depending on the drive pool size it might be a lot more data loss. NAS is usually good until you need a SAN. They are going from SAN to NAS you shouldn't do that if your objective is to keep all data uncorrupted. SAN's are a pain to set up and sync so data integrity is there. The benefit of a SAN is you can have more than just 1PiB of storage but you also get the redundancy of having it be over more pools and with more redundancy. The down side is it cost more to do, more to run, and takes more time to do the monthly data checks happen. The upside is there can be more than just 1PB of addressable storage at a time in a SAN all in RAID and due to the reasons behind why to have a SAN compared to a NAS it will all be able to recover from a data loss too. The parts i have seen take up the most room at those monthly error logs but they are needed for upkeep of the servers to run repair, restore or just replace a drive that failed. The logs are typically .txt files so it takes a while to get big enough to be noticeable but over time it does if you store it all onto one drive location.