On Nov 18, 2015, at 1:01 PM, John R Pierce <pierce at hogranch.com> wrote: > > On 11/18/2015 11:55 AM, Warren Young wrote: >> It’s rather annoying to buy a NAS, then later realize you need to buy*another* NAS as a mirror in case the first one roaches itself. Isn’t that what redundant storage is supposed to avoid? > > > no, RAID is purely availability when faced with single or double drive failure, nothing else. classic raid is most certainly NOT about data integrity, as the raid stripes aren't checksummed, they assume hardware data integrity. I knew I’d get some kind of lecture like that. Look, I know RAID/ZFS is not a backup. My point is simply that if you need to keep a mirror of your file server just in case it roaches itself, what you have there is dual redundancy, not a backup. You need an offline backup *on top* of that, for the same reason that all hot mirrors are not backups. My point is that unreliable NAS/RAID systems *require* this dual redundancy, whereas a reliable system only needs normal backups, that being the sort where you rarely go back and pull more than a few files at a time.