A filesystem for virtualization

Yes, the FMODE_NOCMTIME flag is used on XFS by both xfs_fsr (online defragmentation) to move data around the filesytem without applications noticing it and by xfsdump for when it is pulling data out of the filesystem during backups.

It was also used by HSM applications that used DMAPI, but the invisible IO had nothing to do with the DMAPI interface. i.e the HSMs used the same mechanism as xfs_fsr to move data in/out of the filesystem (to/from tape) without any user visible file data or metadata modification. So while DMAPI is no longer in use, the filesystem utilities still use this flag for moving data around the filesystem without leaving traces that users and applications may get upset about...

-Dave.