Very Computer

I recently installed Linux (Debian woody) on a P4 machine that has two SCSI
disks.  Linux installed well on the second disk (/dev/sdb) which is an IBM
Ultrastar 18GB SCSI disk. Everything seemed perfectly fine with the system
until I attempted to look at the partitions with PartitionMagic.

PartitionMagic reported that the Linux partition had an error.  So, I booted
Linux, ran fdisk and received the following report from "fdisk -l /dev/sdb":

----
Disk /dev/sdb: 1 heads, 35565080 sectors, 1 cylinders
Units = cylinders of 35565080 * 512 bytes

   Device Boot    Start       End    Blocks   Id  System
/dev/sdb1   *         1         1  17652064+  83  Linux
Partition 1 has different physical/logical beginnings (non-Linux?):
     phys=(0, 1, 1) logical=(0, 0, 64)
Partition 1 has different physical/logical endings:
     phys=(1023, 255, 63) logical=(0, 0, 35304192)
Partition 1 does not end on cylinder boundary:
     phys=(1023, 255, 63) should be (1023, 0, 35565080)
----

I never noticed this before, so I decided to run cfdisk.  It showed the
partition as being correct:

---
     sdb1           Boot            Primary     Linux ext2
18075.75
---

and the cfdisk table print produced:

---
Partition Table for /dev/sdb

         ---Starting---      ----Ending----    Start Number of
 # Flags Head Sect Cyl   ID  Head Sect Cyl    Sector  Sectors
-- ----- ---- ---- ---- ---- ---- ---- ---- -------- ---------
 1  0x80    1    1    0 0x83  255   63 1023       63  35304129
 2  0x00    0    0    0 0x00    0    0    0        0         0
 3  0x00    0    0    0 0x00    0    0    0        0         0
 4  0x00    0    0    0 0x00    0    0    0        0         0
---

My big question is why are fdisk and cfdisk reporting different information.
Which is correct?  My Linux installation is working, but this anomaly in the
partition table bothers me.  Might anyone have any information on why this
is occuring?

Many thanks for your time.

Pete Willemsen
University of Utah

Quote:> Hello.

> I recently installed Linux (Debian woody) on a P4 machine that has two SCSI
> disks.  Linux installed well on the second disk (/dev/sdb) which is an IBM
> Ultrastar 18GB SCSI disk. Everything seemed perfectly fine with the system
> until I attempted to look at the partitions with PartitionMagic.

> PartitionMagic reported that the Linux partition had an error.  So, I booted
> Linux, ran fdisk and received the following report from "fdisk -l /dev/sdb":

> ----
> Disk /dev/sdb: 1 heads, 35565080 sectors, 1 cylinders

Quote:> and the cfdisk table print produced:

> ---
> Partition Table for /dev/sdb

>          ---Starting---      ----Ending----    Start Number of
>  # Flags Head Sect Cyl   ID  Head Sect Cyl    Sector  Sectors
> -- ----- ---- ---- ---- ---- ---- ---- ---- -------- ---------
>  1  0x80    1    1    0 0x83  255   63 1023       63  35304129

Having inconsistent CHS geometry is an invitation to disaster. I
therefore recommend that you back up, fix the problem, and restore.
Unfortunately, "fix the problem" is easier said than done. Without
knowing the precise cause of the problem, it's hard to say how to fix
it. As a first stab, though, I'd do this:

1) In Linux, use "dd if=/dev/zero of=/dev/sdb bs=512 count=1". This will
   completely wipe out the partition table, along with any flaky
   information it might contain that could be the root of the problem.
2) Since you mentioned you've got Partition Magic, I'd recommend
   booting it and using it to create new partitions. I believe that PM
   has some way to report the CHS geometry, so check that it doesn't use
   1 for the number of heads or cylinders. If it does, start over or try
   another tool.
3) When you re-install or restore Linux, check with fdisk and cfdisk to
   see that the CHS geometry is being reported consistently.

You might also investigate Linux driver options for your SCSI host
adapter. It's possible that this is caused, at least in part, by a SCSI
driver bug. Post information on what SCSI adapter you're using if you
continue to have problems and post again.

--

http://www.rodsbooks.com
Author of books on Linux & multi-OS configuration

Your suggestions worked great.  I'm still not sure of why cfdisk
initially created my paritions incorrectly. I'll investigate that if I
have time.

In any event, I zeroed out the partition table, had PartitionMagic
create *any* Linux partitions I needed and then I installed Linux.  The
CHS geometry reported by PartitionMagic is now in sync with what fdisk
reports: 2213 Cyl, 255 Heads, and 63 Sectors.

Thanks again for your help.

Pete Willemsen