How to create *exactly* the same partitions in different disks

Norberto Meijome freebsd at
Wed Aug 31 12:13:30 GMT 2005

Glenn Dawson wrote:
> At 12:07 AM 8/31/2005, Norberto Meijome wrote:
> fdisk wants slices to start on a head boundary, and end on a cylinder 
> boundary.
> if you make start evenly divisible by the number of sectors per track, 
> and make size+start evenly divisible by sectors*heads, fdisk won't 
> change any of the numbers on you.
> So, for your disk:
> start / sectors = 332775
> you have size specified as 467427240, so:
> (467427240 + 20964825) / (16 * 63) = 484515.9375
> fdisk will treat that as 484515 and do:
> (16 * 63 * 484515) - 20964825 = 467426295
> and use that number as the new size.

Thanks for the explanation :)

> This matches ad6.  It would appear that ad4 had the start and end values 
> explicitly set causing it to come out with different numbers.

Gotcha. ad6 , ad8 and ad10 (*) , the ones I sliced by hand, follow this 
rule. ad4 doesn't, which is the one that got created by sysinstall on 
the initial setup. I told it to create a slice of 10GB.

So sysinstall doenst follow the rule? Am I missing something here?

I guess i can move all of ad4s1 around to ad6s1, boot off ad6, rebuild 
ad4s1 and move back in... right?

(*) FWIW, all four drives are exactly the same, so the only difference 
is how the slices were done.

ad4: 238475MB <WDC WD2500JS-00MHB0 02.01C03> at ata2-master SATA150
ad6: 238475MB <WDC WD2500JS-00MHB0 02.01C03> at ata3-master SATA150
ad8: 238475MB <WDC WD2500JS-00MHB0 02.01C03> at ata4-master SATA150
ad10: 238475MB <WDC WD2500JS-00MHB0 02.01C03> at ata5-master SATA150


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