Date: Tue, 05 Dec 2000 15:40:20 +0100 From: Siegbert Baude <siegbert.baude@gmx.de> To: "Jose M. Alcaide" <jose@we.lc.ehu.es> Cc: mupi@mknet.org, stable@freebsd.org Subject: Re: The trouble with boot0 Message-ID: <3A2CFE54.674433E6@gmx.de> References: <200012042029.eB4KTDs02259@nordier.com> <00120414014303.00662@mukappa.home.com> <3A2CC2FB.7ACDF0B6@we.lc.ehu.es>
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Hi, don´t have any real documentation, but my experience only on differnces between LARGE and LBA. > LBA = Logical Block Addressing. My understanding is that the modern IDE > disks support this access mode (by sector number instead of CHS specification), > just as SCSI drives work. > > > Large=do away with the BIOS limitations on the size of the CHS designation > > altogether. This allows "straight" CHS access to drives larger than 540MB, LBA always uses the maximum number on heads and sectors. This will make the 1024 cylinder boundary cover an area as big as possible (well-known 8 GB). > My theory about how LARGE mode works is the same. LARGE uses a number of heads (e.g. 128) which reduces the unusable area at the end of the disk, becaus of the limitation to end partitions on cylinder boundaries. This can be some MBs on big disks (therefore the name LARGE ?) > I think that boot0 > fails to boot the same slice which it was able to boot when the > disk is in LBA mode because the geometry used to create the slices > does not match with the real geometry used by the LARGE mode, but > I am not sure of this. Cylinders and sectors have different sizes in LBA and LARGE and therefore the boot-code (addressed in CHS values by the BIOS) is simply not found, thus not executed ;-) Advice: Choose LBA or LARGE at the very beginning of your disks life and never change it (except you´re willing to completely erase all partitions on it). Side note: dmesg spits out the CHS-mapping of LARGE on my disks, which are all formatted with LBA (multi-OS-machine including Win). It seems to use the same code of space optimization as the BIOS. Was confusing for me, when fiddling around with fdisk and disklabel. Does anybody know, if this can be changed? Are this values stored anywhere and then used by fdisk or are they recalculated by fdisk independent of the dmesg values? Ciao Siegbert To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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