Btrfs over RAID10/ZFS for cold backup, does the second checksum just add fragmentation
I use a box for cold backup. Stuff gets there in two ways. Some I upload from my PC, and some are Btrfs snapshots sent over from my other servers. The host already has RAID10 or ZFS underneath, so it already does checksums and keeps redundancy. I still format Btrfs on top myself.
I keep wondering if that second layer actually buys me anything, or if it mostly just leaves me with more fragmentation and extra overhead on small files. Especially with send and receive, I have a lot of small dev files, and I am not sure if that still runs clean when the layer below is already doing checksums.
Has anyone run this double layer setup for a while. What actually broke or slowed down for you in practice. I am more interested in real experience than theory.