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Subject: bug#22496: why does the parted math look wrong - Q1 ?
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Hi,

I need some education on how parted is doing math.  ;-)

The drive is 1 TB.

# parted /dev/rdsk/c7t1d0p0
GNU Parted 2.3.0
Using /dev/rdsk/c7t1d0p0
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) unit cyl
unit cyl
(parted) p
p
Model: Generic Ide (ide)
Disk /dev/rdsk/c7t1d0p0: 121601cyl
Sector size (logical/physical): 512B/512B
BIOS cylinder,head,sector geometry: 121601,255,63.  Each cylinder is 8225kB.
Partition Table: gpt

Number  Start      End        Size       File system  Name  Flags
  1      0cyl       121600cyl  121600cyl               zfs
  9      121600cyl  121601cyl  1cyl

*
Question 1)*

Based on the parted value  8225KB per cylinder,  I would think that 
sectors per cylinder could be calculated thus

     8225 KB/cyl   * 1024 Bytes/KB  = 8422400 Bytes/cyl

and  8422400 Bytes/cyl   / 512 Bytes/sector  = 16450   sectors per cylinder

However, I would also think that sectors per cylinder could be 
calculated thus:
                               
                                                                                               255  * 63  = 16065   sectors per cylinder

Obviously these numbers do not match.

Just for the heck of it, in case when parted says 1 KB it means 1,000 
bytes not 1,024 bytes, I did this math.

     8225 * 1000 = 8225000    / 512 = 16064.4531 sectors per cylinder

which is certainly closer to the value you get from 255 * 63 but it 
really doesn't make any sense to me to be thinking that we are getting a 
fractional number of sectors in a given cylinder.


Thanks for your insight.

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    <font face="Courier New, Courier, monospace">Hi,<br>
      <br>
      I need some education on how parted is doing math.&nbsp; ;-)<br>
      <br>
      The drive is 1 TB.<br>
      <br>
      # parted /dev/rdsk/c7t1d0p0<br>
      GNU Parted 2.3.0<br>
      Using /dev/rdsk/c7t1d0p0<br>
      Welcome to GNU Parted! Type 'help' to view a list of commands.<br>
      (parted) unit
      cyl&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br>
      unit cyl<br>
      (parted)
      p&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br>
      p<br>
      Model: Generic Ide (ide)<br>
      Disk /dev/rdsk/c7t1d0p0: 121601cyl<br>
      Sector size (logical/physical): 512B/512B<br>
      BIOS cylinder,head,sector geometry: 121601,255,63.&nbsp; Each cylinder
      is 8225kB.<br>
      Partition Table: gpt<br>
      <br>
      Number&nbsp; Start&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; End&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Size&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; File system&nbsp; Name&nbsp; Flags<br>
      &nbsp;1&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0cyl&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 121600cyl&nbsp; 121600cyl&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; zfs<br>
      &nbsp;9&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 121600cyl&nbsp; 121601cyl&nbsp; 1cyl<br>
      <br>
    </font><font face="Courier New, Courier, monospace"><b><br>
        Question 1)</b><br>
      <br>
      Based on the parted value&nbsp; 8225KB per cylinder,&nbsp; I would think
      that sectors per cylinder could be calculated thus<br>
      <br>
      &nbsp;&nbsp;&nbsp; 8225 KB/cyl&nbsp;&nbsp; * 1024 Bytes/KB&nbsp; = 8422400 Bytes/cyl&nbsp; <br>
      <br>
    </font><font face="Courier New, Courier, monospace">and&nbsp; 8422400
      Bytes/cyl &nbsp; / 512 Bytes/sector&nbsp; = 16450&nbsp;&nbsp; sectors per cylinder<br>
      <br>
    </font><font face="Courier New, Courier, monospace">However, I would
      also think that sectors per cylinder could be calculated thus:<br>
      &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
      &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
      255&nbsp; * 63&nbsp; = 16065&nbsp;&nbsp; sectors per cylinder<br>
      <br>
      Obviously these numbers do not match.<br>
      <br>
      Just for the heck of it, in case when parted says 1 KB it means
      1,000 bytes not 1,024 bytes, I did this math.<br>
      <br>
      &nbsp;&nbsp;&nbsp; 8225 * 1000 = 8225000&nbsp;&nbsp;&nbsp; / 512 = 16064.4531 sectors per
      cylinder<br>
      <br>
      which is certainly closer to the value you get from 255 * 63 but
      it really doesn't make any sense to me to be thinking that we are
      getting a fractional number of sectors in a given cylinder.<br>
      <br>
      &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br>
    </font><font face="Courier New, Courier, monospace">Thanks for your
      insight. </font><br>
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Subject: bug#22496: Acknowledgement (why does the parted math look wrong -
 Q1 ?)
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Subject: bug#22496: why does the parted math look wrong - Q1 ?
References: <56AD21AC.1060401@HIDDEN>
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I see inconsistent data when printing table. It shoud be:
 Number  Start       End         Size       File system  Name  Flags
 1      0cyl        121600cyl** 121601cyl*               zfs
 9      121600cyl** 121601cyl   2cyl*

* Starting cylinder should be the first cylinder and count in the amount
** Strange ending at same cylinder that other partition begins.

The problem may be partitions aren't created in cylinders (but sectors),
and you try to calculate numbers based on a worng unit now.

On 30/01/16 21:48, Chris Johnson wrote:
> Hi,
> 
> I need some education on how parted is doing math.  ;-)
> 
> The drive is 1 TB.
> 
> # parted /dev/rdsk/c7t1d0p0
> GNU Parted 2.3.0
> Using /dev/rdsk/c7t1d0p0
> Welcome to GNU Parted! Type 'help' to view a list of commands.
> (parted) unit cyl                                                        
> unit cyl
> (parted) p                                                               
> p
> Model: Generic Ide (ide)
> Disk /dev/rdsk/c7t1d0p0: 121601cyl
> Sector size (logical/physical): 512B/512B
> BIOS cylinder,head,sector geometry: 121601,255,63.  Each cylinder is 8225kB.
> Partition Table: gpt
> 
> Number  Start      End        Size       File system  Name  Flags
>  1      0cyl       121600cyl  121600cyl               zfs
>  9      121600cyl  121601cyl  1cyl
> 
> *
> Question 1)*
> 
> Based on the parted value  8225KB per cylinder,  I would think that
> sectors per cylinder could be calculated thus
> 
>     8225 KB/cyl   * 1024 Bytes/KB  = 8422400 Bytes/cyl 
> 
> and  8422400 Bytes/cyl   / 512 Bytes/sector  = 16450   sectors per cylinder
> 
> However, I would also think that sectors per cylinder could be
> calculated thus:
>                              
>                                                                                              
> 255  * 63  = 16065   sectors per cylinder
> 
> Obviously these numbers do not match.
> 
> Just for the heck of it, in case when parted says 1 KB it means 1,000
> bytes not 1,024 bytes, I did this math.
> 
>     8225 * 1000 = 8225000    / 512 = 16064.4531 sectors per cylinder
> 
> which is certainly closer to the value you get from 255 * 63 but it
> really doesn't make any sense to me to be thinking that we are getting a
> fractional number of sectors in a given cylinder.
> 
>       
> Thanks for your insight.

Message sent to bug-parted@HIDDEN:

Subject: bug#22496: why does the parted math look wrong - Q1 ?
Resent-From: "Brian C. Lane" <bcl@HIDDEN>
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Date: Mon, 1 Feb 2016 09:04:20 -0800
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On Sat, Jan 30, 2016 at 03:48:44PM -0500, Chris Johnson wrote:
> Hi,
> 
> I need some education on how parted is doing math.  ;-)

It would probably be better to have this discussion on the devel list,
not the bug tracker:

parted-devel@HIDDEN

AFAIK nobody uses cylinders for anything these days. I certainly haven't
used them for over a decade. Why aren't you using sectors?

As far as understanding the math, you're probably going to have to look
at the code :)

-- 
Brian C. Lane | Anaconda Team | IRC: bcl #anaconda | Port Orchard, WA (PST8PDT)

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