fdisk options actually do
Since I was just looking into this recently, I will write down what I've
learned about the less obvious effects of some of the
- As a side effect of switching to using sectors as
the size unit,
fdiskstops rounding up the end of your partitions to the nearest track or cylinder boundary.
- This stops
fdiskfrom rounding up the start of partitions to the nearest track or cylinder boundary. (Fdisk gives this the cryptic description of turning off "dos compatibility".)
An example may help show the effects:
- with the default settings, a disk with just an extended partition that takes up the whole disk will have it start at sector 63 and end somewhat before the end of the disk.
ualone, the partition will start at sector 63 but run to the end of the disk.
c, the partition will start at sector 1 and run to the end of the disk.
If you care about the exact size of your partitions, for example
because you are trying to get some number of exactly identically sized
partitions, you should use
c is optional but will get you
somewhat more disk space.
(Note that even with sector units and no DOS compatibility
will still silently add one sector to your logical partition sizes,
apparently so that partitions always start on an even sector
number. This is not visible in
fdisk output (which always reports the
size of partitions in Kbytes, regardless of the setting of
have to use a tool like
sfdisk to see the exact details.)
I see no reason not to use
c all the time, with the possible
exception of leaving some disk space at the front of disks for the
bootloader. The tracks and cylinders that
fdisk talks about are purely
imaginary constructs on any disk made since at least the turn of the
century, all of which have much more complicated internal geometries
and actively hide them from you anyways, so you might as well just use
straight sectors (or kilobytes, megabytes, and so on) and dispense with
all the complexity and artificial limitations.