Hello list,

I was getting very slow boot speeds on old WYSE C10LE thin client with VIA C7 CPU and Phoenix bios (year 2008). This is due to combination of BIOS, GRUB, and what I assume Debian-installer bugs.

Long story short, Debian writes strange/incorrect C/H/S values to the MBR partition table upon installation, to which testdisk software complains as "Bad relative sector".

I've tried to install Debian 12 i386 to a 8G disk, using qemu, with guided automatic partitioning. Testdisk data right after the installation:

Disk testz.img - 8589 MB / 8192 MiB - CHS 1045 255 63
Current partition structure:
     Partition                  Start        End    Size in sectors

 1 P Linux                    0  32 33   919 199 48   14774272

Bad relative sector.
 2 E extended               919 232 16  1044  52 32    1996802

Bad relative sector.
No partition is bootable
 5 L Linux Swap             919 232 18  1044  52 32    1996800

Bad relative sector.

It seems that testdisk automatically recalculates C/H/S values and shows corrected data (in the table above).

Here's what really is present in the MBR (data of the first partition entry):

$ ./mbr_my.py testz.img Status: 0x0
C/H/S start:             4 4 1
Part type:               0x83
C/H/S end:               1023 254 2
LBA of first sector:     2048
Sector count:            14774272

fdisk/cfdisk and parted all create partitions for which testdisk does not complain.

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