Installer: no option to set geometry/corrupts partition table

randux at randux at
Sun Mar 4 10:27:09 PST 2007

Matthew Dillon wrote:
:Hi guys,
:I installed the 1.8.0 release from the liveCD and it screwed up my 
:partition table. How can I set the drive geometry so that the installer 
:will use my c/h/s values instead of the (possibly incorrect) values said 
:to be obtained from BIOS?
:I noticed this problem in FreeBSD but it seems to have been mitigated by 
:the installer offering a "G" option to set drive geometry around 6.1/6.2 
:release, not sure exactly when.
:I posted a question on the users list on Feb. 26 but hearing nothing 
:(and wanting to install Dfly 1.8.0 release) I am posting here on bugs. 
:Someone with a multiboot setup who doesn't track changes to his 
:partition table can suffer loss of data because of this error. It could 
:be a relatively serious problem, especially for newbies to multibooting 
:as symptoms probably won't appear immediately, it will be difficult to 

    Hmm. usually that sort of problem is due to the disk mode in the
    BIOS setup not being set to Large or logical block mode.  Nobody
    has used CHS in a long time, and BIOSes still get confused by faked
    CHS numbers.
					Matthew Dillon 
					<dillon at>
Hi Matt,

There needs to be an option such as FreeBSD (and NetBSD and iirc 
OpenBSD) are providing, to set c/h/s for use by the DFly installer. I 
don't understand the comment that nobody is using it- all the *BSD show 
their view of it and if it doesn't match the partition table (which is 
laid out to this day in terms of c/h/s whether it's actual or virtual) 
it causes problems.

For example, my machines are set up with 255 heads 63 sectors and how 
ever many cylinders the drive maps to.  I fdisk the drive and I create 
my partitions aligned on cylinder boundaries. When DFly installs it uses 
16 heads and some other factor for sectors. He changed the units on the 
partition table and this means that the partitions I had created before 
and after (locations, not times) the DFly target slice are no longer on 
integral boundaries, and that writing on the DFly filesystems can leak 
into my other partitions and corrupt data.

There should be a simple way to set the c/h/s in the installer. 
Otherwise it does not play nice in a multiboot scenario.


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