[Mageia-discuss] partitioning bug

[blind Pete]

Pascal Terjan wrote:

> On Fri, Jul 6, 2012 at 8:37 AM, blind Pete
> <0123peter at gmail.com> wrote:
>> David W. Hodgins wrote:
>>
>>> On Thu, 05 Jul 2012 05:10:30 -0400, blind Pete
>>> <0123peter at gmail.com> wrote:
>>>
>>>> Cfdisk is very unhappy about something.
>>>>
>>>>     FATAL ERROR: Bad primary partition 3: Partition begins after
>>>>     end-of-disk Press any key to exit cfdisk
>>>>
>>>> It looks like cfdisk's error message is wrong.  Partition 3 is mounted
>>>> and in use.
>>>
>>>> Disk /dev/sda: 121601 cylinders, 255 heads, 63 sectors/track
>>>> Warning: extended partition does not start at a cylinder boundary.
>>>> DOS and Linux will interpret the contents differently.
>>>> Units = sectors of 512 bytes, counting from 0
>>> 121601x255x63=1953520065
>>
>> CHS has not been reliable since zones were introduced decades ago.
>> They are just a general hint that it is a big drive.  LBA or
>> sector number is all that matters.  What happens inside the HDD
>> case is an unknowable mystery.
> 
> But cfdisk is still based on CHS (or was few years ago).

Ancient history:  

Before the introduction of the ATA hard drive standard, in about 1990, 
the normal way to address a sector was with a CHS tuple.  With ATA 
zone formatting became standard practice.  There are fewer sectors in 
a cylinder near the spindle than in a cylinder near the rim.  The 
Integrated Drive Electronics then "translated" the hidden real, but 
variable, geometry into a pretend geometry with a constant number of 
sectors per cylinder, so that existing operating systems like DOS and 
possibly BIOSes would not fail miserably by being told that 1,1,20 
does not exist, but 20,1,30 is fine.

Aligning things with physical cylinders was sometimes a good idea, but 
now that information is hidden inside the drive.  Aligning things with 
pretend cylinders is pointless, because they probably don't correspond 
to physical cylinders.  

> For example https://bugzilla.redhat.com/show_bug.cgi?id=630340#c1 says
> that 2.18 (the one in mageia 1) expected the size of the device to be
> a multiple of the cylinder size.

There was a bug in cfdisk two years ago.  It seems to have been fixed.  
Mageia 2's cfdisk does not complain about my hard drive.  

>> Even if partition four were past the end of the disk it would not
>> excuse cfdisk for complaining about partition three.
> 
> Yes I don't know why it complains about 3 and not 4

The old version does some invalid maths - and gets the wrong answer.  

-- 
blind Pete
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