Messages in this thread | | | Date | Thu, 17 Jul 2003 17:34:13 +0200 | From | Andries Brouwer <> | Subject | Re: [PATCH] pdcraid and weird IDE geometry |
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On Thu, Jul 17, 2003 at 03:58:38PM +0100, Alan Cox wrote: > On Iau, 2003-07-17 at 15:37, Walt H wrote: > > > On the second drive, it's like this: > > capacity = 80418240, head=255, sect = 63 > > lba = capacity / (head * sect) = 5005 int or 5005.80 float > > lba = lba * (head * sect) = 80405325 int or 80418240.01 float > > lba = lba - sect = 80405262 int or 80418177 float > > Would fixed point solve this. Start from capacity <<= 16 and then > do the maths. That would put lba in 65536ths of a sector which > should have the same result as your float maths
Ach Alan - I have not seen these earlier posts, but float or fixed point here is just nonsense.
The purpose of A = B/C; A *= C; can only be to round B down to the largest multiple of C below it. Using infinite precision just turns this into A = B;
He needs the first sector of the last cylinder, in a setup where cylinders have size 16*63 or so, but the surrounding software thinks that it is 255*63, a mistake.
I don't know anything about these RAIDs, but possibly it would help to give boot parameters for this disk.
Maybe he is victim of the completely ridiculous drive->head = 255; in ide-disk.c. (We have drive->head, the number of physical heads, and drive->bios_head, the translation presently used by the BIOS - or at least that is the intention. It is a bug if the former is larger than 16. The latter may well be 255.)
Andries
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