17.4.a Disk Geometry I - example syntax incorrect.

jengel

The lead-in to the example state the screenshot will show how we can view the geomtery with fdisk. This is then followed with a screenshot NOT showing the geometry using the the command "sudo fdisk -l /dev/sda".

I confirmed in 16.04 and 18.04 Ubuntu installs that this is not correct. Last this command worked were in 16.04 (I only work on LTS version so cannot comment on other versions.

The correct way to view this is with "sudo fdisk -l -u=cyliners /dev/sda"

as per man fdisk:

 

       -u[=unit]
              When listing partition tables, show sizes  in  'sectors'  or  in
              'cylinders'.   The  default  is  to  show sizes in sectors.  For
              backward compatibility, it is possible to use the option without
              the <units> argument -- then the default is used.  Note that the
              optional <unit> argument cannot be separated from the -u  option
              by a space, the correct form is for example '-u=cylinders'.

 

sudo fdisk -l -u=cylinders /dev/sde

Disk /dev/sde: 55.9 GiB, 59961769984 bytes, 117112832 sectors

Geometry: 255 heads, 63 sectors/track, 7289 cylinders

Units: cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

 

coop

That is because it was not done on an Ubuntu system, it was done on a redhat-based distribution.  The distributions have different versions of fdisk, or it has been compiled differently.  If you run fdisk manually, you can type "u" to change units.  If we make the change you request people using other distirbuitons besides ubuntu 18.04 will complain.  This is Linux.  

jengel

Hi,

The whole purpose of the slide is to display geometry in the context of cylinders and the discussion that continue on the next slide while the picture shows nothing about it. It has nothing to do with "This is Linux". 



In the meatime I also checked on RHE 7.4 and there too, sectors is the deault as per your screenshot. When changing unit to cylinders it does use. However, one difference here is that RHE does not display the disk "CHS" information like Ubuntu.  (I tried to attach screenshots but get a messgage about not being authorized.)



using "u" in interactive mode is the same as "-u" on the command line, except for the warning about the use being depricated. 



I don't know what you mean with "this is Linux" and "other distrinution ..... will comnplain".  Your screenshot does not reflect what you are talking about, as simple as that. If it is an issue to show the geometery then drop the screenshot or maybe the entire discussion about CHS. 



 

coop

What is your problem here?  We use screenshots from various distributions throughout the course, even ones we don't really talk about like gentoo, just for variety.  The "this is linux" comment means that there is variation between distributions and even between versions within a distribution, so take everything with a dynamic grain of salt and think rather than pedantically look for every nit.  

Relax.  Every time we do a new version of the course we review the screenshots and use up to date ones if there is a change.  If you know enough to complain about this detail, good for you, but of the thousands of people who take this course noone else was confused.  So it is obviously not a show stopper.

 

 

jengel

Maybe my ESL is hampering me here. I get what you are saying about variations and maybe I don't get what you are trying to say.

I guess we don't need to dwell on the topic. I was simply trying to say if the idea of the slide was to show geometry in the forms of cylinders, heads and sectors (which I thought was the topic) then the slide do not show that as newer versions of the software default to not showing it.

If I misunderstood and you simply wanted to show the sectors only, then my bad.

Either way, I get the topic and fully understand the concept behind C/H/S and LBA.

coop

The whole fdisk geometry thing is becoming kind of irrelevant in the real world, since for SSD's and network storage they are just faked to conform to standards of reporting to programs like fdisk If you do something like:

c7:/tmp>
c7:/tmp>for names in /sys/block/sd? ; do echo $names ; cat $names/queue/rotational ; done
/sys/block/sda
1
/sys/block/sdb
0
/sys/block/sdc
0
c7:/tmp>

you see that on this system only /dev/sda is a conventional hard disk, the others are ssd. I tend to use /sda for pretty static content where I don't care much about performance.

Even in the case of conventional hard disks, the onchip software lies about geometry anyway and does a lot of optimization. The printout of fdisk is rooted in ideas like 15 years old. Personally I only care about the partition placement and size

jengel

Very true. I was surprised even to find any slides on it in modern course. Reminded me of the MFM/IDE days (Seagate ST225??) days and low level formatting drives before one could use it. Then you also had to deal with interleave .....