You're both right and wrong. RAID controllers that you could afford for yourself, costing less than $1000, are just another point of failure. I've seen them fa

You're both right and wrong. RAID controllers that you could afford for yourself, costing less than $1000, are just another point of failure. I've seen them fail more often than the disks, causing corruption as they went. However I've also seen the very expensive datacenter RAID controllers keep a whole bunch of servers up for years as their (15k rpm spinning rust) disks were failing and being swapped. SSD problems with power failure are such that ZFS won't save you. ZFS's checksumming will at least know what's corrupted and what isn't. But the extent of the corruption will be practically unlimited if the OS can't trust the drive to honor write barriers / flushes - any byte since the last powerup could still be only in volatile cache on the SSD and never make it to persistent NAND. Every filesystem depends on these occasional flushes/barriers to establish checkpoints where all previous writes are really written, including ZFS. Consider, it may have created an updated copy of the filesystem tree root node, made sure it was flushed, made another updated copy, made sure it was flushed, and then (only after the flushes) re-used the space that the original copy occupied for other data. If you can't trust that the flushes actually happened when the drive indicated they were completed, then it might be that only the last write, over the original root node copy, actually made it to the NAND.