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Re: qtparted and kernel disagree about partitions



In <134597558.16750431267720927300.JavaMail.root@md01.wow.synacor.com>, 
Stephen Powell wrote:
>On Thu, 4 Mar 2010 10:44:10 -0500 (EST), David Goodenough wrote:
>> I have a hard drive with a primary partition and an extended partiton.
>> QTParted says that it has /dev/hda1, /dev/hda2 and /dev/hda5 which is
>> what one would expect, but when I boot the disk the kernel reports
>> that there are only the /dev/hda1 and /dev/hda2 partitons, no /dev/hda5.
>
>What happened to /dev/hda3 and /dev/hda4?  How can there be a /dev/hda5
>without all the partitions in between?

Using "MS-DOS" partitioning:

1-4 are the Primary partitions.  Their extents are recorded on sector 0 of the 
drive.

5-15 are the Logical partitions.  Their extents are recorded in a partition 
table store inside primary partition (which is not otherwise used).

bss@monster:~% ls /dev/sd[fg]*
/dev/sdf   /dev/sdf5  /dev/sdg   /dev/sdg5
/dev/sdf1  /dev/sdf6  /dev/sdg1  /dev/sdg6

>> The really odd thing is that qtparted is running on the kernel which
>> can not see /dev/hda5.
>
>Perhaps qtparted reads the partition table directly, rather than
>relying on the kernel for this information.

Yes, it does.  It's also possible that the kernel doesn't understand the 
partition table, but qtparted does.

I've never had this happen, but it might be useful to see any kernel messages 
about hda, particularly about partitioning.  These messages would appear in 
/var/log/kern.log, I think.

The output of (parted -l) might also be useful.

It's possible there's a inconsistency in your partition table that qtparted 
corrects but the kernel does not.

>> I do not know how I would access the data in /dev/hda5 if I can not see
>> it).

device-mapper or losetup using /dev/hda as the basis device and a rather 
large, manually calculated offset.

If you just want the bytes backed up, just dd from /dev/hda.
-- 
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