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Date: Fri, 21 Nov 2014 16:00:56 -0700 (MST)
From: Warren Block <wblock@wonkity.com>
To: Nathan Whitehorn <nwhitehorn@freebsd.org>
Subject: Re: Dangerously dedicated mode with FreeBSD 10.1
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Cc: Rostislav Krasny <rosti.bsd@gmail.com>, freebsd-sysinstall@freebsd.org
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On Fri, 21 Nov 2014, Nathan Whitehorn wrote:

>>> This has never been true. It does 4K alignment on disks with 4K physical 
>>> sectors (no matter what the logical sector size is). If you have disks 
>>> with larger sectors or preferred boundaries (e.g. a striped RAID), it will 
>>> also align to that.
>> 
>> I know that it did not automatically do that alignment originally, which 
>> was why I entered PR 161720:
>> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=161720
>> 
>> After that, I thought it was fixed, and now this appears to be a 
>> regression:
>> http://forums.freebsd.org/threads/does-bsdinstall-in-10-1-properly-partition-ssds.48993/ 
>> 
>
> It has done this since initially committed to the tree before 9.0. If you 
> have a drive with 512 byte physical sectors, it will use 512 byte alignment. 
> If you have a 4K drive, it will use 4K alignment. Is there anywhere in those 
> threads where it misaligns a partition? Most of the discussion just seems to 
> be that it does use 512 byte alignment sometimes, which isn't an issue if you 
> have 512 byte sectors.

This might be an "Advanced Format" thing, where the drive uses 4K 
sectors but reports that it uses 512-byte sectors.  The forum thread 
shows that it does not align to 4K on SSDs.  My SSDs also report 4K 
stripesize but only 512 byte sectoresize.