The only thing I can think of is something's updating metadata due to relatime mount option. Maybe try noatime? At 9GiB, really it's 4.5GiB because whatever is being written is being doubled by raid1 profile and multiple devices. There is a case of wandering trees where a little bit of change can get amplified, but this requires an instigator, the file system won't do it on its own.
What were the mkfs options? Are you using the default 16KiB nodesize? --- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
