fdisk question (long)
Ion-Mihai Tetcu
itetcu at apropo.ro
Tue Dec 2 07:56:33 PST 2003
On Tue, 2 Dec 2003 10:10:34 -0500 (EST)
Jerry McAllister <jerrymc at clunix.cl.msu.edu> wrote:
> >
> > Hope someone will have the pacince to read all this ...
> >
> > I have a 120G HDD, in the BIOS is set as LBA. I've RTFM as much as I
> > could, but there still are some things I clearly don't understand. I
> > want to be sure that I can move this disk to another machine with
> > anouter BIOS and the system still boots up.
> >
> > I've used sysinstall to make partitions and the result is bellow:
>
> The basic and general answer to most of this is that nowdays with
> modern disks, the Cylinder/Head/Sector values are essentially fiction.
> They are based on values that can no longer be used with larger
> disks and the system just generates values to make things happy.
> The controllers are able to map the "absolute" sector number to
> the correct place on the disk - which, bny the way, might even be
> remapped due to sector errors and you don't even know it; it doesn't
> tell you about those until there are more bad sectors than it has
> spares for remapping.
I know (end even with SMART I don't like it - You usally find out about
it when nothing can be done).
> Just go by the total number of sectors. Let fdisk do its thing.
> It does it right. Do not try to set any Cylinder/Head/Sector
> values. Ignore that part of things. For all practical purposes,
> that part of things is obsolete. Even though some parts of the
> system still fiddle with it, nothing really happens with it. About
> the only thing it might want is for slices to begin and end on
> cylinder boundaries and since you really can't control those, just use
> the numbers it gives you as a divider to make sure your proposed slice
>
> size comes out even and then go with it.
What I fail to see is the corespondence between sector and capacity in
something like MB or KB.
> So, choose the slice sizes you want by total number of blocks/sectors
> and then use the -t switch to see what happens just to make sure the
> sizes work out the way you want and then trust fdisk to do what is
> right.
>
> > it# fdisk ad0
>
> Try doing"
> "fdisk -s ad0"
>
> To read the disk information. It gives you all the information that
> is usually meaningful and is less confusing.
I did:
it# fdisk -I ad0
******* Working on device /dev/ad0 *******
it# fdisk -s ad0
/dev/ad0: 232578 cyl 16 hd 63 sec
Part Start Size Type Flags
1: 63 234438561 0xa5 0x80
So: 234438561+63 = 234438624
If I add the sizes in sectors from the previous I get
sysinstall 234436545
fdisk-by-hand 234436482
The difference is exactly 63 and none match with this new one.
Why ?
> > Media sector size is 512
> > Warning: BIOS sector numbering starts with sector 1
> > Information from DOS bootblock is:
> > The data for partition 1 is:
> > sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
> > start 63, size 497952 (243 Meg), flag 0
> > beg: cyl 0/ head 1/ sector 1;
> > end: cyl 30/ head 254/ sector 63
> > The data for partition 2 is:
> > sysid 6 (0x06),(Primary 'big' DOS (>= 32MB))
> > start 498015, size 41929650 (20473 Meg), flag 0
> > beg: cyl 31/ head 0/ sector 1;
> > end: cyl 1023/ head 254/ sector 63
> > The data for partition 3 is:
> > sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
> > start 42427665, size 192008880 (93754 Meg), flag 0
> > beg: cyl 1023/ head 255/ sector 63;
> > end: cyl 1023/ head 254/ sector 63
> > We haven't changed the partition table yet. This is your last
> > chance. parameters extracted from in-core disklabel are:
> > cylinders=232578 heads=16 sectors/track=63 (1008 blks/cyl)
> >
> > Figures below won't work with BIOS for partitions not in cyl 1
> > parameters to be used for BIOS calculations are:
> > cylinders=232578 heads=16 sectors/track=63 (1008 blks/cyl)
> >
> > Information from DOS bootblock is:
> > 1: sysid 0 (0000),(unused)
> > start 0, size 497952 (243 Meg), flag 80 (active)
> > beg: cyl 0/ head 0/ sector 1;
> > end: cyl 493/ head 15/ sector 63
> > 2: sysid 6 (0x06),(Primary 'big' DOS (>= 32MB))
> > start 498015, size 41929650 (20473 Meg), flag 0
> > beg: cyl 31/ head 0/ sector 1;
> > end: cyl 1023/ head 254/ sector 63
> > 3: sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
> > start 42427665, size 192008880 (93754 Meg), flag 0
> > beg: cyl 106/ head 15/ sector 1;
> > end: cyl 127/ head 14/ sector 63
> > 4: <UNUSED>
> > Should we write new partition table? [n] y
--
IOnut
Unregistered ;) FreeBSD user
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