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Date:      Sat, 6 Dec 2008 15:31:49 -0800
From:      "Peter Wemm" <peter@wemm.org>
To:        "Marcel Moolenaar" <xcllnt@mac.com>
Cc:        FreeBSD Arch <arch@freebsd.org>
Subject:   Re: RFC: making gpart default
Message-ID:  <e7db6d980812061531q7f33ed0fm35f6191d3975fe8f@mail.gmail.com>
In-Reply-To: <5783CEB0-6163-429E-8B28-2F9D6FBCF4A8@mac.com>
References:  <e7db6d980811291356w54256e6du82350baf3c57d591@mail.gmail.com> <e7db6d980812011605h18b40700v1043e376ef392365@mail.gmail.com> <20081203.193714.693830802.imp@bsdimp.com> <200812041313.34565.jhb@freebsd.org> <5783CEB0-6163-429E-8B28-2F9D6FBCF4A8@mac.com>

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On Thu, Dec 4, 2008 at 3:08 PM, Marcel Moolenaar <xcllnt@mac.com> wrote:
>
> On Dec 4, 2008, at 10:13 AM, John Baldwin wrote:
>
>> No, the way GPT works, you have a PMBR at sector 0, then immediately
>> following
>> that you have the Primary partition table in the next N sectors (the first
>> sector in the table has a header that contains the size of the table).
>>  Then
>> you have a backup Secondary partition table in the last N sectors of the
>> disk
>> as well.  At least with the old gpt(8) tool you could actually tell it how
>> big of a table to make when you created a GPT, and I imagine gpart
>> probably
>> can do the same.
>
> Yes. For schemes that support it, you can specify how many entries
> to allocate. The 34 corresponds to 128 entries for GPT (4 entries
> per sector)...


Yes.
1 sector (pmbr)
1 sector (header)
32 sectors (128 partitions)
= 34 sectors.

Or we could have
1 sector (pmbr)
1 sector (header)
62 sectors (248 partitions)
= 64 sectors.

At least it is a power of two, even if only 32K.  I'd love it if the
man page told users to reserve another 32K for "boot code", so that
the start address becomes sector 128, or 64K.  This is a commonly used
stripe size.

-- 
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com; KI6FJV
"All of this is for nothing if we don't go to the stars" - JMS/B5
"If Java had true garbage collection, most programs would delete
themselves upon execution." -- Robert Sewell



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