[wellylug] Help - Confusing partitions

Cliff Pratt enkidu at cliffp.com
Sun Feb 18 12:03:20 NZDT 2007


Cliff Pratt wrote:
> Carl Turney wrote:
>> Hi Folks,
>>
>> OPTIONAL BACKGROUND INFO:
>>
>> I'm a relative newbie to LINUX, running Fedora Core 5 myself.  With
>> help from a Wizard in Melbourne, I set up a fast, thorough, easy, and
>> neat backup system, using removable IDE hard disks.  (Basically it
>> involved partitioning, initialising, and Grubbing a second physical
>> drive, then using elegant -tar- commands (once) to create a backup
>> copy, followed by regular -rsync- commands to keep the backup
>> up-to-date.  A bit of manual editing of configuration files is also
>> required.  If anyone is interested, I can email you my step-by-step
>> notes on this.)  Actually, I have =two= backup drives, and alternate
>> between both of them, because a "lightning strike" can happen in the
>> middle of a backup, killing both disks.
>>
>> It works perfectly, and I've even used it to migrate to larger 
>> drives/partitions.  A "complete restore" takes ~5 minutes, including
>>  powering down, finding & inserting the backup disk, and booting up.
>>
>> THE SITUATION:
>>
>> New to Welly, my landlady/housemate is Lyndsay (on this list).  I'm 
>> starting to set up the same backup scheme with her Ubuntu 5.10
>> system, which was set up by Peter Black (possibly on this list?)
>> about a year ago.  But the partitioning and usage of the original
>> (working) Ubuntu hard disk has me confused.  Here...
>>
>> (fdisk report:)
>>
>> Disk /dev/hda: 40.0 GB, 40020664320 bytes 255 heads, 63
>> sectors/track, 4865 cylinders Units = cylinders of 16065 * 512 =
>> 8225280 bytes
>>
>> Device Boot      Start         End      Blocks   Id  System /dev/hda1
>> *           1        1216     9767488+  83  Linux /dev/hda2
>> 1420        1543      996030   82  Linux swap / Solaris /dev/hda4
>> 1544        4852    26579542+   f  W95 Ext'd (LBA) /dev/hda5
>> 1544        4852    26579511   83  Linux
>>
>> (df report:)
>>
>> Filesystem           1K-blocks      Used Available Use% Mounted on 
>> /dev/hda1              9614116   1897216   7228528  21% / tmpfs
>> 258244         0    258244   0% /dev/shm tmpfs
>> 258244     12588    245656   5% /lib/modules/2.6.12-10-386/volatile 
>> /dev/hda5             26162008   3348468  21484568  14% /home
>>
>> FINALLY... MY QUESTIONS:
>>
>> (1) Is it important that there is no hda3 partition?
>>
> A disk can normally have up to 4 primary partitions or 1 to 3 primary
> partitions and one extended partition with as many logical partitions as
> you like. (I've vague memories of BSD violating this rule, somehow).
> 
> If there is an extended partition the partition are numbered primary one
> to three and extended four, with any logical partitions from 5 up, even
> if (as is the case here) when there are fewer than three primary
> partitions. So, no, it is not important that there is no hda3.
 >
Further, this is an architecture that goes back to the early days of 
hard disks. It is usually complied with, for compatibility reasons, but 
I don't believe that it is set in concrete. It depends on, among other 
things, the capabilities of your disk formatter, I believe.
 >
>>
>> (2) Should I expect any difficulty in creating an hda4 partition
>> without creating an hda3 first, using fdisk?
>>
> No, the extended partition will be hda4. I think there has to be one
> primary partition at least, though.
>>
>> (3) Is hda5 truly a =logical= LINUX partition, created within a 
>> =physical= Windows partition, hda4?  (Note same start & stop
>> cylinders.)
>>
> It's not Windows, it's 'extended'. There is no OS at this level. The 
> extended partition contains logical partitions.
>  >
>> (4) Could the logical hda5 be created using LINUX's fdisk, as I 
>> seriously doubt that any genuine Micro$oft Windows utility would
>> offer creation of a logical LINUX partition?
>>
> Yes, if you create an extended partition, then a logical partition 
> within it, the first one will be hda5. This is true of Windows fdisk 
> too, except that the partition type won't be Linux.
 >
To clarify, Windows numbers the partition in the same order, though of 
course it doesn't call them 'hda1' etc.
 >
>  >
>> (5) Would Ubuntu be able to "seamlessly" work, if I bypassed the
>> Windows hda4 partition altogether?
>>
> It's nothing to do with Windows. Yes, you can create the disk with no 
> extended partition, and just root, swap and home all as primary partitions.
>  >
>> (6) What possible benefits are there to such a "logical within a 
>> physical" setup, in the original (working) hard disk?
>>
> If you want more than four partitions, you have to use an extended 
> partition, eg:
> 
> /dev/hda1    primary
> /dev/hda2    primary
> /dev/hda3    primary
> /dev/hda4    extended, contains the following
> /dev/hda5
> /dev/hda6
> ....
> 
> The fact that /dev/hda2 and /dev/hda3 may be missing confuses those new 
> to disk partitioning. In your setup there is no advantage in the 
> extended partition.
> 
> Cheers,
> 
> Cliff
> 
> 




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