GNU bug report logs - #22496
why does the parted math look wrong - Q1 ?

Previous Next

To reply to this bug, email your comments to 22496 AT debbugs.gnu.org.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Chris Johnson <cj <at> tothemax.us>
To: bug-parted <at> gnu.org
Subject: why does the parted math look wrong - Q1 ?
Date: Sat, 30 Jan 2016 15:48:44 -0500

[Message part 1 (text/plain, inline)]

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 part 2 (text/html, inline)]

Message #8 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Narcis Garcia <debianbugs <at> actiu.net>
To: bug-parted <at> gnu.org
Subject: Re: bug#22496: why does the parted math look wrong - Q1 ?
Date: Sun, 31 Jan 2016 18:16:48 +0100

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 #11 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Brian C. Lane" <bcl <at> redhat.com>
To: bug-parted <at> gnu.org
Cc: cj <at> tothemax.us
Subject: Re: bug#22496: why does the parted math look wrong - Q1 ?
Date: Mon, 1 Feb 2016 09:04:20 -0800

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 <at> lists.alioth.debian.org

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)

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.