[curt15]

>- ability to turn off checksumming for specific files

This is something that has always confused me. BTRFS users are always advised to disable copy-on-write (thus preventing checksumming or compression) for VM images or database files to avoid massive performance hits from fragmentation. Even Facebook still stores its databases mostly on XFS filesystems. However, the ZFS community seems to indicate that you can achieve reasonable performance for databases and VMs just by tuning the recordsize (e.g. https://pg.uptrace.dev/zfs/). How does ZFS mitigate the problems from fragmentation?