[debbugs-tracker] bug#22497: closed (parted math - Q2 and Q3 ?)

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Your message dated Mon, 8 Feb 2016 08:56:06 -0500
with message-id <address@hidden>
and subject line Re: bug#22497: parted math - Q2 and Q3 ?
has caused the debbugs.gnu.org bug report #22497,
regarding parted math  - Q2 and Q3 ?
to be marked as done.

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22497: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=22497
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--- Begin Message --- Subject: parted math - Q2 and Q3 ? Date: Sat, 30 Jan 2016 17:03:49 -0500 User-agent: Mozilla/5.0 (X11; SunOS i86pc; rv:10.0.6esrpre) Gecko/20120731 Thunderbird/10.0.6

# 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 2)

Based on the parted information shown above, I would assume that the Total Sectors could be calculated thus:

                    121601 * 255 * 63 = 1953520065
Indeed, gparted  shows this value when you look at the disk device information.

Alas, when I switch to units of sectors I get a different value!!!

(parted) unit s                                                          
unit s
(parted) p                                                               
p
Model: Generic Ide (ide)
Disk /dev/rdsk/c7t1d0p0: 1953525168s   <---------
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start        End          Size         File system  Name  Flags
 1      256s         1953508750s  1953508495s               zfs
 9      1953508751s  1953525134s  16384s



Question 3)

When I look at the information above where units are sectors, it is clear that the "End" sector number is the last sector being used in the partition.  This is supported in the above example by the fact that partition 9's first sector number is one higher than the End sector number of partition 1.

Alas, when looking at the information in units of cylinders, it seems like there is a change in meaning.

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

If there are  121600 cylinders in partition 1  and the first of those is cylinder number 0, I would expect the ENDing cylinder number to be 121599.
This expectation would also seem reasonable given that the starting cylinder number for partition 9 is 121600.

Hmmm, perhaps what I am looking at is how parted displays information when partitions are not sized to end on a cylinder boundary?

It likely is the case that partition 1 does not nicely end with the last sector of cylinder 121599 but instead has some sectors in cylinder 121600 and furthermore that partition 9's starting sector is also in cylinder 121600 ... 
Is that what's going on here?

Given that this drive is SSD and the whole cylinder,head,sector thing is all a mirage, I assume there is no value to trying to align the partitions to cylinder boundaries.
 
Thanks for your insight.

--- End Message ---

> --- Begin Message ---
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> Subject: 
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> Re: bug#22497: parted math - Q2 and Q3 ?
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> Date: 
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> Mon, 8 Feb 2016 08:56:06 -0500
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> User-agent: 
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> Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1
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> On 1/30/2016 5:03 PM, Chris Johnson wrote:
> > It likely is the case that partition 1 does not nicely end with the last
> > sector of cylinder 121599 but instead has some sectors in cylinder
> > 121600 and furthermore that partition 9's starting sector is also in
> > cylinder 121600 ...
> > Is that what's going on here?
> > 
> > Given that this drive is SSD and the whole cylinder,head,sector thing is
> > all a mirage, I assume there is no value to trying to align the
> > partitions to cylinder boundaries.
>
> Yes.  The bottom line is: don't use cylinder mode.  It is a 30 year old
> anachronism that is now just a lie with no basis in reality.
>
>
>
>
> --- End Message ---