FAQ Search Today's Posts Mark Forums Read
» Video Reviews

» Linux Archive

Linux-archive is a website aiming to archive linux email lists and to make them easily accessible for linux users/developers.


» Sponsor

» Partners

» Sponsor

Go Back   Linux Archive > Gentoo > Gentoo User

 
 
LinkBack Thread Tools
 
Old 09-03-2008, 06:57 AM
Alan McKinnon
 
Default Partition schme question

On Wednesday 03 September 2008 05:57:47 Jarry wrote:
> Alan McKinnon wrote:
> >> dd if=/dev/sda2 of=/dev/null
> >> 957169664 bytes (957 MB) copied, 17.5531 s, 54.5 MB/s
> >>
> >> dd if=/dev/sda12 of=/dev/null
> >> 820854784 bytes (821 MB) copied, 21.4136 s, 38.3 MB/s
> >
> > What do you conclude from this?
>
> I'd say that /dev/sda2 is near "beginning" of disk (outer side,
> more sectors per cylinder, higher transfer speed), and /dev/sda12
> is near "end" of disk (inner side, less sectors per cylinder,
> lower transfer speed).

Ah, I see my troll caught one already. You seem to be under the common
delusion that the structure reported by fdisk actually means something about
the physical disk :-)

These days the entire concept of a "cylinder" is a mere abstraction to make
tools like fdisk work in a sane manner.

But yes, it does seem that in this case sda2 is probably near the outer edge
of the platter where the head speed relative to the disk is higher.
--
alan dot mckinnon at gmail dot com
 
Old 09-03-2008, 11:53 AM
Matthias Bethke
 
Default Partition schme question

Hi Alan,
on Wed, Sep 03, 2008 at 08:57:42AM +0200, you wrote:
> These days the entire concept of a "cylinder" is a mere abstraction to make
> tools like fdisk work in a sane manner.

Of course not. The disk is physically organized in cylinders, that's the
structure dictated by the mechanical design. That a disk controller is
theoretically free to map cylinders and sectors to whereever it pleases
doesn't mean that there wasn't a direct relationship between cylinder
number and physical location on the platter in the vast majority of
non-broken (i.e. cylinder-remapped) disks. With many HD tests in
magazines you get a cylinder-vs.-transfer-rate plot and it still mostly
matches the old rule. I suppose not even firmware hackers are really
eager to make things more complicated than absolutely necessary

cheers,
Matthias

--
I prefer encrypted and signed messages. KeyID: FAC37665
Fingerprint: 8C16 3F0A A6FC DF0D 19B0 8DEF 48D9 1700 FAC3 7665
 
Old 09-03-2008, 12:17 PM
Alan McKinnon
 
Default Partition schme question

On Wednesday 03 September 2008 13:53:09 Matthias Bethke wrote:
> Hi Alan,
>
> on Wed, Sep 03, 2008 at 08:57:42AM +0200, you wrote:
> > These days the entire concept of a "cylinder" is a mere abstraction to
> > make tools like fdisk work in a sane manner.
>
> Of course not. The disk is physically organized in cylinders, that's the
> structure dictated by the mechanical design. That a disk controller is
> theoretically free to map cylinders and sectors to whereever it pleases
> doesn't mean that there wasn't a direct relationship between cylinder
> number and physical location on the platter in the vast majority of
> non-broken (i.e. cylinder-remapped) disks. With many HD tests in
> magazines you get a cylinder-vs.-transfer-rate plot and it still mostly
> matches the old rule. I suppose not even firmware hackers are really
> eager to make things more complicated than absolutely necessary

I disagree on the detail. It's true enough that the data is written in
concentric circular patterns following the apparent path the head follows.
However, outer tracks contain more sectors than inner tracks.

fdisk reports the same size per cyclinder regardless of it's number. So what
fdisk calls a cylinder cannot possibly map exactly to a physical circular
track.

Putting this in firmware is no big deal. If you have 100,000 sectors and
10,000 tracks, then sectors 0-9 are cylinder 0, sectors 10-19 make cylinder 1
etc etc. A simple calculation translates between the two plus a lookup table
to account for marked badblocks. This is grossly over-simplified but you get
the idea.

However, it does make the most sense to keep fdisk's cylinders in some sort of
sequential order, so low numbered cylinders will in all probability end up
near one edge and high numbered cylinders at the other edge.

I strongly suspect that you know this also, and we actually do have the same
understanding of how it works :-)

--
alan dot mckinnon at gmail dot com
 
Old 09-03-2008, 04:14 PM
Matthias Bethke
 
Default Partition schme question

Hi Alan,
on Wed, Sep 03, 2008 at 02:17:07PM +0200, you wrote:
> However, it does make the most sense to keep fdisk's cylinders in some sort of
> sequential order, so low numbered cylinders will in all probability end up
> near one edge and high numbered cylinders at the other edge.
>
> I strongly suspect that you know this also, and we actually do have the same
> understanding of how it works :-)

Yes, now I'm pretty sure we do

cheers,
Matthias

--
I prefer encrypted and signed messages. KeyID: FAC37665
Fingerprint: 8C16 3F0A A6FC DF0D 19B0 8DEF 48D9 1700 FAC3 7665
 
Old 09-03-2008, 04:18 PM
Jarry
 
Default Partition schme question

Alan McKinnon wrote:

dd if=/dev/sda2 of=/dev/null
957169664 bytes (957 MB) copied, 17.5531 s, 54.5 MB/s
dd if=/dev/sda12 of=/dev/null
820854784 bytes (821 MB) copied, 21.4136 s, 38.3 MB/s

What do you conclude from this?

I'd say that /dev/sda2 is near "beginning" of disk (outer side,
more sectors per cylinder, higher transfer speed), and /dev/sda12
is near "end" of disk (inner side, less sectors per cylinder,
lower transfer speed).


Ah, I see my troll caught one already. You seem to be under the common
delusion that the structure reported by fdisk actually means something about
the physical disk :-)


Correct me if I'm wrong, but I do not remember saying anything like
that. And frankly, I can not image how you came to that conclusion.
I just said /dev/sda2 is probably on the outer side, and /dev/sda12
on inner side, based on that difference in transfer speeds...

These days the entire concept of a "cylinder" is a mere abstraction to make
tools like fdisk work in a sane manner.


Partially correct. True is, C/H/S numbers in fdisk does not have any
practical meaning these days. But there are still cylinders, heads
and sectors on disk. And total number of sectors reported by fdisk
is the same, as real total number of sectors on disk. These sectors
are numbered starting first with the most outer tracks on disk on
all physical cylinders, continuing towards the inner most track.
This holds true for nearly all sata/pata-disks. Maybe scsi/sas
have different sector numbering scheme...

But yes, it does seem that in this case sda2 is probably near the outer edge
of the platter where the head speed relative to the disk is higher.


Well, I'd say head speed does not anything to do with it. What makes
transfer rate on the outer tracks of disk faster is higher number of
sectors per cylinder, because nowadays disks have about constant
"bit-density" (only "about" constant, because number of sectors
per cylinder is a discrete number)...

Jarry

--
__________________________________________________ _____________
This mailbox accepts e-mails only from selected mailing-lists!
Everything else is considered to be spam and therefore deleted.
 
Old 09-03-2008, 07:22 PM
Alan McKinnon
 
Default Partition schme question

On Wednesday 03 September 2008 18:18:26 Jarry wrote:
> > Ah, I see my troll caught one already. You seem to be under the common
> > delusion that the structure reported by fdisk actually means something
> > about the physical disk :-)
>
> Correct me if I'm wrong, but I do not remember saying anything like
> that. And frankly, I can not image how you came to that conclusion.
> I just said /dev/sda2 is probably on the outer side, and /dev/sda12
> on inner side, based on that difference in transfer speeds...

Well, I did say "seem" and I could be mistaken.


--
alan dot mckinnon at gmail dot com
 

Thread Tools




All times are GMT. The time now is 01:02 AM.

VBulletin, Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO ©2007, Crawlability, Inc.
Copyright 2007 - 2008, www.linux-archive.org