[ale] duplicating the partition layout?

[Joseph A Knapka]

Joe Steele wrote:
> 
> I had meant to say something about this when I saw the earlier post,
> but I forgot. :(

Thanks very much for the clarification. I didn't realize
there were additional sectors allocated for extended
partitions. I think that explains Robert's results.

Cheers,

-- Joe Knapka

> If you have extended partitions, there are additional partition
> tables which you must duplicate.
> 
> Here's a sample disk layout using fdisk ('p' command):
> --------
> Disk /dev/hda: 32 heads, 63 sectors, 6978 cylinders
> Units = cylinders of 2016 * 512 bytes
> 
>    Device Boot   Begin    Start      End   Blocks   Id  System
> /dev/hda1            1        1        3     2992+  83  Linux native
> /dev/hda2            4        4     6978  7030800    5  Extended
> /dev/hda5            4        4       69    66496+  82  Linux swap
> /dev/hda6           70       70     6978  6964240+  83  Linux native
> --------
> 
> If we enter expert mode ('x' command), the 'p' command gives this:
> --------
> Disk /dev/hda: 32 heads, 63 sectors, 6978 cylinders
> 
> Nr AF  Hd Sec  Cyl  Hd Sec  Cyl   Start    Size ID
>  1 00   1   1    0  31  63    2      63    5985 83
>  2 00   0   1    3  31  63 1023    604814061600 05
>  3 00   0   0    0   0   0    0       0       0 00
>  4 00   0   0    0   0   0    0       0       0 00
>  5 00   1   1    3  31  63   68      63  132993 82
>  6 00   1   1   69  31  63 1023      6313928481 83
> --------
> Of course heads and cylinders are numbered beginning with 0, sectors
> begin with 1.  Each sector contains 512 bytes, and for this disk,
> each head contains 63 sectors, and each cylinder contains 32 heads.
> 
> The main partition table is stored at H/S/C=0/1/0.  The first
> partition follows it at the beginning of the next head, 1/1/0.
> 
> But this disk has two other partition tables. Pointers to those
> additional tables are listed with the 'e' command in expert mode:
> --------
> Disk /dev/hda: 32 heads, 63 sectors, 6978 cylinders
> 
> Nr AF  Hd Sec  Cyl  Hd Sec  Cyl   Start    Size ID
>  2 00   0   1    3  31  63 1023    604814061600 05
>  5 00   0   1   69  31  63 1023  13305613928544 05
>  6 00   0   0    0   0   0    0       0       0 00
> --------
> The second partition table is at H/S/C=0/1/3.  The table's offset (in
> sectors) from the beginning of the disk is (C * 32 + H) * 63 + S - 1
> = 6048.  Looking back at the output of the 'p' command, you see this
> table is sandwiched between the end of the first partition and the
> start of the fifth.
> 
> The third partition table is at 0/1/69.  The table's offset from the
> beginning of the disk is 139104.  The table is sandwiched between the
> end of the fifth partition and the beginning of the sixth.
> 
> To completely duplicate the partitioning from hda to hdb (assuming
> the disks have identical geometries):
> 
> dd if=/dev/hda bs=512 count=1 of=/dev/hdb
> dd if=/dev/hda bs=512 count=1 of=/dev/hdb skip=6048 seek=6048
> dd if=/dev/hda bs=512 count=1 of=/dev/hdb skip=139104 seek=139104
> 
> The more partitions you have, the more complicated this method of
> duplication is likely to get.
> 
> --Joe
> 
> -----Original Message-----
> From:   Robert L. Harris [SMTP:Robert.L.Harris at rdlg.net]
> Sent:   Monday, October 22, 2001 12:33 PM
> To:     Joseph A Knapka
> Cc:     Robert L. Harris; Atlanta Linux Enthusiasts
> Subject:        Re: [ale] duplicating the partition layout?
> 
> Odd...
> 
> Just did this and I get something odd.  My source disk has 8
> slices (not my choice).
> 
> 1-3 linux primary
> 4   extended
> 5-8 linux logical
> 
> After the dd command my target drive has this:
> 1-3 linux primary
> 4   extended
> 5   unknown (some very strange cylinder numbs also).
> 
> ?
> 
> Thus spake Joseph A Knapka (jknapka at earthlink.net):
> 
> > "Robert L. Harris" wrote:
> > >
> > > I have to duplicate a bunch of disks.  They need identicle partition
> > > layouts.
> > >
> > > I don't want to dd if=/dev/sda of=/dev/sdb since we're only actually
> > > using 2 of the 18 gigs right now.
> >
> > dd if=/dev/sda of=/dev/sdb bs=512 count=1
> >
> > ought to do it. You just need to copy the first 512 bytes.

-- 
# "You know how many remote castles there are along the
#  gorges? You can't MOVE for remote castles!" - Lu Tze re. Uberwald
# Linux MM docs:
http://home.earthlink.net/~jknapka/linux-mm/vmoutline.html

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