Comment by dv_dt
6 years ago
Just to further explore that a bit, would you say replication adds independent copies for failures of media, while backup adds copies made by independent software against failures of process / software / media.
6 years ago
Just to further explore that a bit, would you say replication adds independent copies for failures of media, while backup adds copies made by independent software against failures of process / software / media.
Replication increases risk of data loss when implemented incorrectly, because added resources increase the probability of bit errors. This applies to both replicated disks (RAID) and servers. Replicated servers must use ECC memory as well as checksum blocks and periodically scrub data to ensure integrity (e.g. what ZFS does for you). If they don't then a bit error corrupts the data on all servers, because you have no way of know which copies are pristine or how to piece together pristine parts.
Replication covers durability (and availability) in face of system or media failure but does nothing whatsoever against software bugs or human error.