HD geometry - FreeBSD & Gentoo & Windows don't agree.

Drysh

I have a SATA HD Maxtor 6Y120M0.

I'm trying to install Windows, FreeBSD, and Gentoo on this machine. FreeBSD tells me to set the CHS = 14946/255/63 , linux says CHS=238216/16/63. If I chose one, the other OS gives me a warning that the partitions don't end on cylinders boundaries (or something like this). Seagate/Maxtor site says the CHS should be what gentoo fdisk suggests.

What should I use?

NeddySeagoon · Posted: Sat May 12, 2007 11:03 pm Post subject:

Drysh,

The C/H/S addessing scheme is only useful for the first 4Gb of any hard drives. Modern BIOSes and all drives bigger than 4Gb use LBA.
The warning is of historical interest only and may be safely ignored provided you don't want to install any 16 bit OS, like DOS, Windows 3.1 and Windows 95

Drives don't have a Geometry any longer either. They are zoned, with the number of sectors per track changing from zone to zone.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Drysh · Posted: Sat May 12, 2007 11:21 pm Post subject:

I know the C/H/S isn't used anymore, but fdisk reports a problem with my partitions: when I press v to verify, it says the partitions are wrong. Should I ignore fdisk warning?

Aparently FreeBSD changed the geometry stored in the partition table, so the linux and windows partitions are wrong now (acording to gentoo fdisk). I can use the advanced mode of fdisk to set it back to the original values, but then the BSD installer says the BSD partition may overlap my linux partition. The warnings made me think that fdisk uses the fake geometry for something.

My idea is: use linux fdisk to create the partitions and find a way to install bsd without changing the partition scheme (only creating new slices, not partitions). Is it safe? Any idea how to do that?

alex6z · Tux's lil' helper Joined: 20 Jul 2005 Posts: 119

Do I have this right?:

1)SOFTWARE(dos, lilo, grub) -(a)--> BIOS -(b)--> HDD controller/dirve.
2)SOFTWARE(os kernel) -(b)---> HDD
== BIOS access methods ==
(a1) CHS disk access through BIOS interface. Limited to 8.4GB with a translating BIOS and 528MB with a non translating BIOS.
(a2) Interface to bios through extensions, practically unlimited. The BIOS almost always uses LBA access mode for the dirve in this case.

== Drive access modes ==
(b1) CHS - can access 528 MB. Do some dirves support 256 virtual heads and allow up to 8.4GB access??
(b2) LBA access mode. Allows up to something like 220GB. LBA48 fixes this.

Do I have that right?

NeddySeagoon · Posted: Sun May 13, 2007 11:55 am Post subject:

alex6z,

Thats a reasonable summary but its not complete. I'll refer you to the whole history lesson in http://tldp.org/HOWTO/Large-Disk-HOWTO.html#toc1.

The problem at 528Mb came about because the C/H/S numbers were compressed into 24 bits by both the BIOS and the drives but the division of the 24 bits was not the same for the BIOS and drive. Thus 528Mb was the maximum that could be addressed using the bits common to both.

Drysh,

You can ignore the warning that that partitions do not start/end on cylinder boundaries if you will not be installing any 16 bit OS using C/H/S addressing. Look very carefully at starting and ending block numbers. Some partition tools still assume that cylinder boundaries matter and may assign some space to two partitions. You really should not be using one of them.
Providing that your partitions do not overlap and you will not use 16 bit OS, you won't have problems.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.