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If the Linux kernel detects the presence of some disk manager
on an IDE disk, it will try to remap the disk in the same way
this disk manager would have done, so that Linux sees the same
disk partitioning as for example DOS with OnTrack or EZ-Drive.
However, NO remapping is done when a geometry was specified
on the command line - so a
If you are hit by this, and know someone who can compile a new
kernel for you, find the file
The remapping is done by trying 4, 8, 16, 32, 64, 128, 255 heads
The details are as follows - subsection headers are the strings appearing in the corresponding boot messages. Here and everywhere else in this text partition types are given in hexadecimal.
EZ-Drive is detected by the fact that the first primary partition
has type 55. The geometry is remapped as described above,
and the partition table from sector 0 is discarded - instead
the partition table is read from sector 1. Disk block numbers
are not changed, but writes to sector 0 are redirected to sector 1.
This behaviour can be changed by recompiling the kernel with
OnTrack DiskManager (on the first disk) is detected by the fact that the first primary partition has type 54. The geometry is remapped as described above and the entire disk is shifted by 63 sectors (so that the old sector 63 becomes sector 0). Afterwards a new MBR (with partition table) is read from the new sector 0. Of course this shift is to make room for the DDO - that is why there is no shift on other disks.
OnTrack DiskManager (on other disks) is detected by the fact that the first primary partition has type 51 or 53. The geometry is remapped as described above.
An older version of OnTrack DiskManager is detected not by partition type, but by signature. (Test whether the offset found in bytes 2 and 3 of the MBR is not more than 430, and the short found at this offset equals 0x55AA, and is followed by an odd byte.) Again the geometry is remapped as above.
Finally, there is a test that tries to deduce a translation
When Linux detects OnTrack Disk Manager, it will shift all disk
accesses by 63 sectors. Similarly, when Linux detects EZ-Drive,
it shifts all accesses of sector 0 to sector 1.
This means that it may be difficult to get rid of these disk managers.
Most disk managers have an uninstall option, but if you need to remove
some disk manager an approach that often works is to give an explicit
disk geometry on the command line. Now Linux skips the
The details depend a little on kernel version. Recent kernels (since 2.3.21) recognize boot parameters like "hda=remap" and "hdb=noremap", so that it is possible to get or avoid the EZD shift regardless of the contents of the partition table. The "hdX=noremap" boot parameter also avoids the OnTrack Disk Manager shift.
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