gpart, to -a 4k or to -b 1M

Warren Block wblock at
Sat Nov 16 14:05:14 UTC 2013

On Sat, 16 Nov 2013, Shane Ambler wrote:

> On 16/11/2013 10:46, Warren Block wrote:
>> On Fri, 15 Nov 2013, aurfalien wrote:
>>> 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.

It doesn't hurt anything.  By rounding both starting location and length 
to 1M multiples, it still forces 4K alignment.

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