It looks like a number of newer drives are going to a 4K physical
sector size (but retaining the 512 byte logical sector size for
the interface). Properly aligned operations wind up being more
efficient.
So here's the issue for us. The fdisk program initializes slice 1
starting at (512 byte) sector #63 instead of 64 in order to align
to the system's idea of a cylinder boundary. This is due to
the 63 sectors/track value:
cylinders=242251 heads=256 sectors/track=63 (16128 blks/cyl)
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,(DragonFly/FreeBSD/NetBSD/386BSD)
start 63, size 3907024065 (1907726 Meg), flag 80 (active)
beg: cyl 0/ head 1/ sector 1;
end: cyl 1023/ head 255/ sector 63
The data for partition 2 is:
The question is, can we safely modify fdisk to start the
slice in the second sector of the cylinder instead of the
first (cyl 0 head 1 sector 2) in order to align it to
logical sector #64?
It's a one-line fix in the fdisk program. The question is
whether doing that retains compatibility for booting PCs.
Presuming that PCs support LBA or LARGE mode it should work,
theoretically. I haven't tried booting from such a disk yet.
-Matt
Matthew Dillon
<dil...@backplane.com>
diff --git a/sbin/fdisk/fdisk.c b/sbin/fdisk/fdisk.c
index fbdad7d..38b970f 100644
--- a/sbin/fdisk/fdisk.c
+++ b/sbin/fdisk/fdisk.c
@@ -373,7 +373,7 @@ main(int argc, char *argv[])
partp = (struct dos_partition *) (&mboot.parts[0]);
partp->dp_typ = DOSPTYP_386BSD;
partp->dp_flag = ACTIVE;
- partp->dp_start = dos_sectors;
+ partp->dp_start = (dos_sectors + 63) & ~63;
if (disksecs - dos_sectors > 0xFFFFFFFFU) {
printf("Warning: Ending logical block > 2TB, using max
value\n");
partp->dp_size = 0xFFFFFFFFU;
