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Date: Sat, 16 Nov 2013 16:08:15 +1030
From: Shane Ambler <FreeBSD@ShaneWare.Biz>
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To: Warren Block <wblock@wonkity.com>, aurfalien <aurfalien@gmail.com>
Subject: Re: gpart, to -a 4k or to -b 1M
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On 16/11/2013 10:46, Warren Block wrote:
> On Fri, 15 Nov 2013, aurfalien wrote:
> 
>> Hi,
>>
>> Curious, for best practice in ensuring 4K alignment, should one do;
>>
>> gpart add ... -b 1M
>>
>> or
>>
>> gpart add ... -a 4k
>>
>> Thank in advance,
> 
> They do different things.  '-b 1M' starts the added partition at 1M but
> does not force it to be a multiple of 4K in size.
> 
> '-a 4k' forces the added partition to start at the next 4K-aligned
> block, and forces the size to be a multiple of 4K.
> 
> I recommend both for the first filesystem partition, and '-a 4k' for
> later ones.

I believe it was related to windows co-existence but I heard a while
back that -a 1M is a good option to use.