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    SubjectRe: ATA 4 KiB sector issues.
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    On Wed, 2010-03-17 at 00:20 +0900, Tejun Heo wrote:
    > On 03/17/2010 12:02 AM, James Bottomley wrote:
    > > On Tue, 2010-03-16 at 23:50 +0900, Tejun Heo wrote:
    > >> e.g. If the first partition begins at CHS 0/32/33 and ends at
    > >> 12/233/19 and the corresponding LBA addresses are 2048 and 206848, you
    > >> can solve the equation and determine that the parameters gotta be 63
    > >> secs/trk and 255 heads/cyl to make those two pairs of addresses match
    > >> each other and in fact some BIOSs try to do this depending on
    > >> configuration (and sometimes falls into infinite loop or causes other
    > >> boot related problems if the parameters are too uncommon).
    > >
    > > for an msdos label, this is illegal, that was Arnd's point. The
    > > partitions have to begin and end on cylinder boundaries*. Knowing that,
    > > you can deduce the geometry from the last sector entry.
    > >
    > > * at least if you want to preserve windows compatibility, which is what
    > > most of our partitioning tools seem to do.
    >
    > Well, the thing is that
    >
    > * Anything remotely modern (>= XP) doesn't give a hoot about cylinder
    > alignment.
    >
    > * Anything older (<= 2000) is very likely to get confused with custom
    > geometry starting from the BIOS itself. For those cases, the only
    > thing we can do is aligning partitions to cylinders abiding BIOS
    > supplied geometry parameters which will usually be 255/63.
    >
    > So, using custom geometry doesn't help compatibility at all.

    Our partitioning tool still obey the integral cylinder rule ... we can
    argue about whether they should, but what we need is a strategy for
    fixing what is rather than what should be.

    James



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