> > 2. The allocation time for raw devices is by far better (near
> > instantaneous) than creating preallocated files in a
> > fs. Providing 1 Tb of raw devices is a task of minutes,
> > creating 1 Tb filsystems with preallocated 2 Gb files is a
> > task of hours at best.
>
> Filesystem dependent, surely? Veritas' VxFS can create filesystems
> quickly, and quickly preallocate space for the files.
And you are sure, that this does not create a sparse file, which is exactly
what we do not want ? Can you name one other example ?
> > 3. absolute control over writes and page location (you don't want
> > interleaved pages)
>
> As well as a filesystem, most large systems I'm familiar with use
> volume management software (VxVM, LVM, ...) and their "disks" will be
> allocated space on disk arrays.
Of course. My thinking has long switched to volume groups and logical
volumes. This however does not alter the fact, that one LV can be
regarded as one mainly contiguous (is that the word ?) block on disk
for optimization issues. When reading a logical volume sequentially
head movement will be minimal.
Andreas