Advanced Format Drive ?
Warren Block
wblock at wonkity.com
Thu Nov 15 06:10:05 UTC 2012
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. A good overall reference on GPT is
the Wikipedia page: http://en.wikipedia.org/wiki/GUID_Partition_Table
Remember that the man page is a reference, not a tutorial. I wanted
more specific notes that followed best practices, and that was the
source for this article:
http://www.wonkity.com/~wblock/docs/html/disksetup.html
In general, you create a "partition scheme" first. This can be MBR,
GPT, or others. (But use GPT.)
Rather than combine the bootcode with the partition table, GPT just uses
a small partition for it. Since the standard GPT allows for up to 128
partitions, there's no reason not to use them.
Next come other partitions for UFS or ZFS filesystems or swap.
That's it, really. The rest is details the man page can explain, like
additional options for alignment. (The creation of the first UFS
partition in the article does not use -a because older versions of gpart
did unexpected things when -a and -b were combined. The alignment
produced is correct.)
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