System Management in Control
Certo Certius
more surely than sure
The disk "High Water Mark" (FHM) can be swithed on and off.
When the operating system allocates disk blocks for a file, it automatically sets a highwater mark.
The highwater mark indicates how far the file has been written in its allotted space on the disk.
All blocks in the file up to the highwater mark are guaranteed to have been written since they were
allocated to the file. Users are not permitted to read beyond the highwater mark and thus cannot read
stale data that they did not actually write.