[Mageia-discuss] partitioning bug

[blind Pete]

andre999 wrote:

> blind Pete a écrit :
>> andre999 wrote:
>>
>>    
>>> blind Pete a écrit :
>>>      
>>>> David W. Hodgins wrote:
>>>>
>>>>
>>>>        
>>>>> On Fri, 06 Jul 2012 04:03:34 -0400, blind Pete
>>>>> <0123peter at gmail.com>   wrote:
>>>>>
>>>>>
>>>>>          
>>>>>> Morgan Leijström wrote:
>>>>>>
>>>>>>            
>>>>>>> It would also be interesting to know what other tools say.
>>>>>>> gparted?
>>>>>>>
>>>>>>>              
>>>>>
>>>>>          
>>>>>> Gparted looks pretty.  As far as I can see, gparted agrees
>>>>>> with what I think things should look like.  Gparted and
>>>>>> fdisk agree about the number of sectors.  (More than you
>>>>>> get by multiplying CxHxS.)
>>>>>>
>>>>>>            
>>>>> Interesting.  I guess it would be best to use 'hdparm -i /dev/sda|grep
>>>>> LBAsects" to find out the number of sectors.
>>>>>
>>>>> Regards, Dave Hodgins
>>>>>
>>>>>          
>>>> [root at live ~]# hdparm -i /dev/sda | grep LBA
>>>>    CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953523055
>>>> [root at live ~]#
>>>>
>>>> Same number of sectors as gparted and fdisk report.  Number of heads
>>>> and sectors per cylinder are just, "it's a big disk".  _Posssibly_
>>>> number of cylinders gives a clue about how big.  H can be 63 or 255,
>>>> depending on mood, and CxHxS should be a little less than max LBA.
>>>>
>>>> The situation just got worse.  The latest work arround is to lie
>>>> about how big a sector is.  That is called "advanced" formatting.
>>>>
>>>>        
> 
>>> BTW, with all those partitions, I would convert your disk to GPT tables
>>> instead of MBR, using gdisk.
>>> (gdisk is in core.)
>>>      
>> OK I have installed gdisk and will look at it.  How would you rate
>> it for maturity?  And what else can recognize a gpt disk?
> 
> I would say very mature, even when I started using it (under mdv 2010.0
> or 2010.1)
> The developer says the "hybid" option which simulates MBR for Msw is
> risky, but even that I found very stable and predictable

I let it loose on my test machine.  It has Lilo on the mbr.  Mageia 1 
with Grub in its root partition, Mageia 2 with Grub in its root 
partition, and Ubuntu 10.04.4 with Grub 2 in its root partition.  

Converting to gpt confused Ubuntu's Grub 2.  

Experimenting with a hybrid system, converting a primary 
to a logical, adding a new primary, and renumbering confused 
lots of things.  

It was only the test computer.  

>> Grub?
>>    
> Yes, since 1.97 patched for GPT, as used in mdv and fedora (at least)
> when I started using GPT.
> Mageia has always used this version.
>> Grub2?
>>    
> Definitely

I managed to confuse it.  Posibly by having it installed in the 
root partition.  

>> Lilo?
>>    
> Not sure.  I think newer versions do.

Mostly works.  The mbr code just jumps to a hardcoded sector 
address and loads the real code from what is normally /etc/map.  

>> The Mageia installer?
>>    
> I didn't have a problem.  I did an upgrade install from mdv2010.2 to
> mga1, and could read the other partitions to set up fstab.
> Sometime before mga1 was available, I had a problem which corrupted my
> system, and made it unbootable.  It took me a while to get around that,
> as I didn't want to loose my uncorrupted partitions.  I ended up fixing
> it with SystemRescueCD (it contains a partition recovery tool called
> testdisk.)  I was able to reinstall mdv.  I may have formatted / with
> SystemRescueCD.  At that point I had a "hybrid" format simulating MBR
> for systems not aware of GPT.

Is there any option in the installer to turn the disk into a gpt disk?  

>> Other installers?
>>    
>> Other operating systems?
>>    
> According to what I have read, most other major distros handle GPT
> nicely.  The Linux kernel does.
> Msw 32-bit does not, but can work with gdisks' "hybrid" format, which
> puts an MBR table at the end of the first sector (a space not used by
> GPT).  It is a little tricky to set up, but initially I had it working.
> Recently I haven't been bothered to get it working again.
> Msw 64-bit is GPT-aware, but I have read that it works only on EFT
> hardware, which has a special BIOS.  (Incompatible with Msw 32-bit.)  It
> may be just that it is the default installation.
> MacOS handles GPT, but I'm not sure of the restrictions if any.  Is was
> an early adopter.
> *BSD systems should handle GPT just like Linux.
>>> It will make your disk more stable.
>>> It uses a 128 partition table,with a backup table at the end of the
>>> drive. No such thing as "extended" partitions.
>>> It takes less space than the ms-compatible MBR partition tables.
>>> The only trick is that you need to leave space for the backup table (34
>>> 512-byte sectors).
>>> If you change your mind, you can convert back painlessly.
>>> I've used GPT for over 2 years, including converting back and forth a
>>> few times at first.
>>>
>>> To convert, you'll have to boot to a live disk, preferably with gdisk.
>>> I use systemRescueCD for that. http://www.sysresccd.org/
>>> The latest stable version is 379 Mib, usable from CD or USB key.
>>> I don't know if a Mageia live cd, or Mageia DVD in rescue mode might
>>> work.
>>>      
>> In Mageia 1 the installer pulled it from the net rather than from
>> the local iso, so it was not prepackaged.
> 
> I installed mga1 from DVD.  This upgrade went very smoothly.
> 
> I did have a problem changing partition parameters with diskdrake under
> mga1, not long after installing it, shortly after mga1 was released.
> Luckily I was testing things, so I didn't loose anything important.  But
> everything was lost on the partition in question.  I then tried
> reformatting the partition with diskdrake, and it wouldn't work.  I had
> to use SystemRescueCD (with gparted).
> I strongly suspect it was due to my having a "hybrid" format.  I think
> that at least at that point, diskdrake (or whatever it uses) would see
> the MBR table, and classify the disk as MBR.  While still getting the
> partition location parameters from the GPT table.  (The simulated MBR
> table puts most partitions in a large "foreign" partition.  The
> corrupted partition was not in the MBR table.  And no other partition
> was affected.)
> 
> Note that I have never had a problem simply accessing (read or write) a
> GPT partition on mdv or mga.
> 
> Also, initially I used gdisk to format usb drives (but no hybrid MBR
> table), and have never had a problem on those disks with diskdrake or
> any other mdv or mga tools.
> 
> BTW, I installed gdisk from upstream on mdv, and first imported gdisk to
> Mageia.
>>> Just in case you might be interested
>>>      
>> I'm interested.
> 
> You will probably find this interesting :)
> http://en.wikipedia.org/wiki/GUID_Partition_Table

Thanks.

-- 
blind Pete
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