Changing disk geometry with fdisk

Question

I have a Sun X2100 server that I am attempting to add a second disk to. I want to use SVM to mirror the root disk to the new disk. I made sure that the new disk was the same part number (540-6595) as the existing root disk. Both disks have a label that says "SATA 80GB 7200RPM" and both have the same part number on them, yet once I installed the new disk, I discovered that the new disk has different geometry than the first disk. The original disk reports "cyl 38735 alt 2 hd 64 sec 63" while the new disk reports "cyl 9718 alt 2 hd 255 sec 63".
The fact that two disks with the same part number have different geometry leads me to believe that the geometry must be soft and therefore can be modified. And after reading the man page for the fdisk command, I am further convinced of this. The "-S" argument looks like it will allow me to write out a different geometry to the second disk and make it match the root disk. However, it does not appear to have any affect.
I used the following command to read the geometry from the first disk: "fdisk -W /tmp/geom /dev/rdsk/c1d0p0". Then I used this command to write that geometry to the second disk: "fdisk -S /tmp/geom /dev/rdsk/c2d0p0". But nothing happens. There are no error messages or anything, but when I look at the target disk, it is the same as before.
Has anyone else attempted to do this or know anything about why two disks with identical part numbers have different geometry?
By the way, I have a couple other X2100 servers that were purchased with two disk drives in them. All have the same part number (540-6595) and all disks have the same geometry as my target server's root disk: "cyl 38735 alt 2 hd 64 sec 63".
Thanks,
-Mark

Answer 1

That is true, but I can't lay out physical partitions on disks using sectors as the size specifier. Physical partitions have to end on cylinder boundaries. Since there are fewer cylinders on the second disk but the disks are the same size (80G), the cylinders are larger on the second disk. The result of that is that I cannot create partitions on the second disk that are exactly the same size as their counterpart on the first disk; one of them is going to be slightly larger than the other. That is okay as long as the source mirror is smaller than the target mirror. But having the partitions on the second disk all being slightly larger than their counterparts on the first disk means that, eventually, one partition has to end up being smaller than its counterpart if I am using the entire disk. So that means that SVM will not mirror a partition on the first disk to a smaller partition on the second disk.
The bottom line here is that I need the geometry to match, or at a minimum, the cylinder counts need to be exact multiples of each other. It looks like the fdsik command should allow me to modify the geometry on a disk, but so far I have ben unsuccessful in making it work.
-Mark