@garycase: Thanks for reminding me of the checksum plugins for unRAID. As you mention they appear to only detect corrupt files, not correct them. The data integrity systems of ZFS and Btrfs and SnapRAID also use checksums for detecting errors, but they appear to also be able to fix these silent errors before they are carried on to parity, and before they could be copied to a backup. I can see that I didn't mention this error correction part of the data integrity system used by some of the other NAS solutions in my original post, although I intended to. The silent error correction feature is what arose my initial concern about bitrot in unRAID vs these other systems. The link in my first post shows a comparison table made by the author of SnapRAID were he points out some of these differences. And yes, I am aware that RAID or parity only protects against drive failure, not theft, fire, user error and so forth - only an off site backup would help in those scenarios. I'm very, very pleased to hear that you haven't heard of any cases of bitrot in your time on this board garycase. It does appear to be somewhat overstated then.
@Frank1940: Thanks for pointing out that error correction features are also built into hard drives. Being new to NAS it's not always easy to know how critically important each feature of the different NAS solutions are. Although I must admit I like the idea of data integrity checks through checksum and silent error correction as used by ZFS, Btrfs and SnapRAID, I am more drawn to unRAID as it has many of the other features I desire, like: to read a single file in unRAID only the storage drive where it is saved must spin up. In ZFS and Btrfs all drives must spin up as all files are striped across the drives. And if redundancy should somehow fail only the data on the faulty drive(s) is lost in unRAID where all data is lost on all drives with ZFS and Btrfs. And then there is the ability to use drives of different sizes in unRAID which is very nice feature for a home user like myself who already has a stack of drives and likes to add drives incrementally. Only SnapRAID appears to have some features similar to unRAID while also having data integrity through checksum and silent error correction before parity. Come to think of it, SnapRAID is also open source, perhaps unRAID could adopt a few of its alluring data integrity features in a future upgrade? Thanks for adding to the choir of happy unRAID users Frank
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Thanks to both of you for taking time to comment! An active forum with users happy to help and welcome newcomers into the flock is so valuable!
PS: I'm working this weekend which is why I'm a bit slow to reply.