Re: [vox-tech] Partition Questions Part 2

[Mark Kim <mkkim@ucdMAPSavis.edu>]

On Wed, 6 Dec 2000, Robert G. Scofield wrote:

> It appears that Disk Druid works in terms of megabytes, and that Fdisk
> works in terms of blocks.  I can think in terms of megabytes, but
> I can't think in terms of blocks.  What is a block?  What is the ratio
> between megabytes and blocks; that is, how many bytes are in a block or
> how many blocks are in a megabyte?

You can tell fdisk to use megabytes.  When specifying how much to reserve
the disk space, type "+###M" (without the quotes), where ### is some
number in megabytes.

> I'm not sure about this, but I read something like LILO has to be
> installed below the 1204th cylinder.  What is a cylinder?

Get a vinyl record and look for "rings" on it (the circular
grooves).  There are these ring-equivalent things on hard drives called
"cylinders".  They're called "cylinders" instead of "rings" because a hard
drive has several disks inside, and if you find the same "level" of ring
on each disk then it forms a cylinder shape... or that's how I think of
it.

> Fdisk has entries like this:  Start 149    End 620.  Do these numbers
> refer to cylinders?

Apparently.  The last "End" entry matches the total number of cylinders on
my system.

> If not, how do you know if you're below 1204 (or
> whatever the number is)?

Use the "p" command.  It tells you, on the top, how many cylinders the
disk has.  If it's less than 1024, then give it a big sigh of relief.  If
it's not, then try to make sure the root is somewhere above where it looks
like it'll fit under 1024.

My /dev/hda has 1247 cylinders, according to fdisk:

   Command (m for help): p

   Disk /dev/hda: 255 heads, 63 sectors, 1247 cylinders
                                         ^^^^^^^^^^^^^^
   Units = cylinders of 16065 * 512 bytes

      Device Boot    Start       End    Blocks   Id  System
   /dev/hda1             1       261   2096451    6  FAT16
   /dev/hda2           262       268     56227+  81  Minix / old Linux
   /dev/hda3   *       269       399   1052257+  83  Linux
   /dev/hda4           400      1247   6811560    5  Extended
   /dev/hda5           400       432    265041   82  Linux swap
   /dev/hda6           433      1247   6546456   83  Linux

So... I have my root partition (/dev/hda3) below the 1024 limit because
the later parts of my disk is much larger.  Also /dev/hda3 ends at 399th
cylinder.

> How do you know which numbers to start from and which numbers to end at
> when you are creating partitions on Fdisk?

Start with 1 increase sequentially.  Doing it any other way may confuse
the system.  Did I ever tell you about how Linux's fdisk and MS's fdisk
got into confusion and how I accidentally deleted partitions I wanted to
keep but survived through using quick wit and cunning?

You can only have 4 primary partitions (/dev/hda1 through /dev/hda4).  You
can have extended partitions (/dev/hda5 through /dev/hda16) if you
sacrifice one primary partition (see above -- my /dev/hda4 has been
sacrificed so I can have /dev/hda5 and /dev/hda6).  The reason for this
rule is because initially Microsoft made an oversight that people
probably wouldn't want more than 4 partitions... then they changed their
minds and decided to add extended partitions, which we now make use of
under the Linux world for happily goodness.

-Mark

---
Mark K. Kim
http://www.cbreak.org/mark/
PGP key available upon request.