[RndTbl] drive partitioning for Linux install

Dan Martin ummar143 at cc.umanitoba.ca
Fri Oct 7 16:29:09 CDT 2005

John Lange wrote:

>On Tue, 2005-10-04 at 22:03 -0500, Dan Martin wrote:
>>It turns out that my BIOS and ATA interface cannot handle HDs bigger 
>>than 137 GB, so I am switching my new larger drives to another computer 
>>and using its drives in the P3 - ie, lots of copying drives and partitions.
>I could be wrong here, its been a while, but, so long as your first
>primary partition was below the maximum size your bios allows I think
>you should be able to boot from it. Once linux takes over it will be
>able to see beyond the bios limit.
>Hopefully someone else on this list can provide better information.
I believe this is true, at least for the newer kernels.  However, I 
can't see more than 137GB with Mandrake 8.1 (a 2.4 kernel) nor Windows 
2000 pro sp3.  I turns out there are tweaks to be made to Windows to get 
it to work which I did not make on that system.  I suspect, however, 
that the main problem is my ATA interface.  In fact, I was ordering a 
BIOS but I was advised by a technician (from esupport.com) that this 
would not solve my problem.

>>1)  I need to copy a primary partition on one drive to a logical 
>>partition on another.  I assume that if I do something like this:
>># dd if=/dev/hdc3 of=/dev/hda7 bs=1M
>>that the boot sector of the primary will overwrite partition info in the 
>>boot sector of the logical partition, destroying extended partition 
>>info.  Is there a way around this?  If I create the logical partition 
>>with Partition Magic under DOS and copy into it, skipping the first 
>>sector, will that work?
>No, dd moves the raw data between any two character devices. /dev/hdc3
>does not have a "boot sector", only /dev/hdc does. Moving data between
>partitions regardless if they are logical or primary should be fine.
I believe primary partitions do have boot sectors, containing a stage 1 
loader for whatever OS might be on the partition.  There is only boot 
code, no partition tables since they are contained in the MBR.

>However, if you instead did 
># dd if=/dev/hdc of=/dev/hda7 bs=1M
>then you would have a problem since you are moving between a raw device
>and a partition. I don't think /dev/hda7 would be mountable at that
>point (never tried it).
>But you would be able to reverse the process and it would be usable. 
The reverse would overwrite the MBR.

To restate the question:

Primary partitions have a boot sector that may or may not containing 
loading instructions (in fact I think there is a whole track at the 
start which is not part of the filesystem proper).  Logical partitions 
may start with such code as well, but they also "contain" a partition 
table like that of the MBR, but with only 2 records filled to indicate 
the address of the partition and that of the next logical partition in 
the chain.  It would be disastrous to overwrite this table by copying a 
primary partition into it, or even a (incorrect) table from another 
logical partition.

Therefor, I assume that "hda7" starts after the partition table adjacent 
to the partition table associated with hda7, and will not be overwitten 
by copying another device's characters into it.  Is this true?

I didn't take a chance - I used Partition Magic to transform a primary 
partition into a logical one.  This process took approximately 16 hours 
for a 75GB partition!

>>2)  I also installed Linux in my P4.  When Linux complained it couldn't 
>>read the partition tables for sda, I let it rewrite them, thinking this 
>>was the new drive I put in.  Instead, it was my serial ATA drive array.  
>>I have it configured to show up as one large drive under Windows.  A 
>>large number of ATI video files were stored on the drive, which shows up 
>>in Linux as 2 drives (unallocated) and continues to show up in Windows 
>>as 1 drive - but now unallocated.
>>The original drive was partitioned as a single FAT32 partition for the 
>>whole drive.  My guess is that the data is still intact, and could be 
>>recovered if I put the right partition info onto the boot sector.
>>Is there a simple way to recover this?  If I created a new FAT32 
>>partition in the "unallocated" space using Partition Magic in DOS or 
>>Windows, is that likely to recover the data?
>First of all, you should use LVM (making two drives appear as one) with
>extreme caution. If EITHER of the drives fail there is a good chance you
>will loose all your data on both drives.
I believe I did this in hardware, not Windows LVM, but Linux does not 
seem to recognize it.

>Second, I really can't answer this question regarding how it works in
>Windows but I will offer this; when you alter the partition scheme it
>doesn't affect any of the data on the drives. Assuming you can put the
>partitions back to exactly the way they were everything still be there.
I'm going to try repartitioning in PM under Windows (which sees this as 
a single drive), and hope it doesn't do even rudimentary formatting of 
my "new" partiiton.


Dr. Dan Martin, MD, CCFP, BSc, BCSc (Hon)

GP Hospital Practitioner
Computer Science grad student
ummar143 at cc.umanitoba.ca
(204) 831-1746
answering machine always on

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