On 11/15/12 12:41, Ronald F. Guilmette wrote:

In message <alpine.bsf.2.00.1211142250370.58...@wonkity.com>,
Warren Block <wbl...@wonkity.com> wrote:

On Wed, 14 Nov 2012, Ronald F. Guilmette wrote:

I'm looking at the examples section of the gpart(8) man page.  May I
assume that if I just want to merely ``try out'' GPT... you know...
taking it out on the road for a first time test run... that I can
just do the first five (5) commands listed under EXAMPLES and then
that will be enough to go ahead and try installing FreeBSD into the
created freebsd-ufs partition?

Even assuming that the answer is yes, I have still more questions...
Where are these magic numbers coming from??  I am specifically talking
about the number "34" in the "-b 34" option and also the number "162"
in the "-b 162" option.  Tha man page just tosses those into the example
command lines without saying a word about them.  And you can probably
guess what it is that is especially troubling to me about them... neither
one of them is divisible by 8 (i.e. 4KB/512B).  So would the examples
in the current gpart(8) man page produce an Epic Fail when and if they
were used with a modern "Advanced Format" drive?

-b is the beginning block of a partition.  34 is a magic value, the size
of a standard GPT partition table.

It probably wouldn't have hurt anything to mention that in the gpart man
page.

And what about 162?  Is that magic too?  If so, how?  I seriously do not
know.

The man example should be taken as a whole. You've got

/sbin/gpart add -b 34 -s 128 -t freebsd-boot ad0

which gives you a 128 block partition starting at block 34, so the next free block is 162, and the next partition is explicitly started there in

/sbin/gpart add -b 162 -s 1048576 -t freebsd-ufs ad0

No magic, just arithmetic. :-)
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