Adam:
Thanks a bunch! That's exactly what the problem is. Soime time ago I changed my IDE connections, but neglected to change the BIOS. hda used LBA addressing, but hdc used AUTO, which defaulted to CHS. This explains some of life's mysteries, like why 2 identical drives appear different.
I will have to look at partitions on my P4, since the BIOS is set to AUTO for those, and the drives have both DOS and Linux partitions. I hope those partition tables are consistent.
I assume the need for LBA settings is relevant only if 1) using DOS, or, 2) using LILO since Linux does not depend on the BIOS addressing.
Is there ever a good reason to NOT use LBA? [perhaps installing an ancient drive with stuff on it partitioned under an old scheme?] In theory, files could be arranged by cylinder to minimize seek times, but in fact the CHS geometries are not "real" anyways, so no benefit there.
Thanks again.
Adam Thompson wrote:
Short answer: turn on LBA support in your BIOS. Don't use 'auto' or 'large drive support', if you can avoid it, and especially avoid 'chs' settings.
That may not be sufficient, it depends on what version of DOS you're running.
Unfortunately, if you turn on LBA (or LBA32) mode, your partition table will be scrambled... but even worse, if you boot from DOS it will still read sector 0 from the drive and infer geometry from what it finds there, not from the BIOS. The easiest way around this is to turn on LBA, then immediately install Windows 2000 or Windows XP or Linux. Don't even try booting DOS until you've successfully recreated the partition table under a more advanced OS. Do NOT try "fixing" things with PartitionMagic at this point, it will just make a worse mess.
(If you boot a Linux kernel, during the boot sequence it identified the disks it found. Output from 'dmesg' should indicate "hda: ....." and it should show some sort of indication as to whether the disk geometry is in C/H/S mode or LBA mode.)
You might want to read the Large Disk HOWTO, found at: http://www.tldp.org/HOWTO/Large-Disk-HOWTO.html as it discusses the sort of thing that I think you're running into.
-Adam