Partition does not end on cylinder boundary

[David]

On 4 June 2011 21:50, Timothy Murphy <gayleard at eircom.net> wrote:
[Partition does not end on cylinder boundary]
> Does this matter?
> If so, what can you do about it?
> I get it after partitioning with fdisk,
> choosing partitions of size 50GB, etc.

The message refers to an attempt to describe the end sector using an
assumed/fictional number of cylinders, heads, sectors/track. Probably
there are not enough bits in the CHS fields to accomodate a disk of
the size you are using. Linux uses LBA and does not care about CHS.
Some bootloaders require correct CHS values but only to locate the
start, not the end.

"""
There is no known operating system that requires this restriction.
However, there exists software that tries to guess the disk geometry
by looking at the CHS start and end values in a partition table. Note
that with large disks CHS values are entirely meaningless.
"""[1]

"""
In a DOS type partition table the starting offset and the size of each
partition is stored in two ways: as an absolute number of sectors
(given in 32 bits) and as a Cylinders/Heads/Sectors triple (given in
10+8+6 bits). The former is OK - with 512-byte sectors this will work
up to 2 TB. The latter has two different problems. First of all, these
C/H/S fields can be filled only when the number of heads and the
number of sectors per track are known. Secondly, even if we know what
these numbers should be, the 24 bits that are available do not
suffice. DOS uses C/H/S only, Windows uses both, Linux never uses
C/H/S.

If possible, fdisk will obtain the disk geometry automatically. This
is not necessarily the physical disk geometry (indeed, modern disks do
not really have anything like a physical geometry, certainly not
something that can be described in simplistic Cylinders/Heads/Sectors
form), but is the disk geometry that MS-DOS uses for the partition
table.

Usually all goes well by default, and there are no problems if Linux
is the only system on the disk. However, if the disk has to be shared
with other operating systems, it is often a good idea to let an fdisk
from another operating system make at least one partition. When Linux
boots it looks at the partition table, and tries to deduce what (fake)
geometry is required for good cooperation with other systems.
"""[2]

[1] http://www.win.tue.nl/~aeb/partitions/partition_types-2.html
[2] man fdisk