Dangerously dedicated mode with FreeBSD 10.1

[Nathan Whitehorn]

On 11/21/14 15:00, Warren Block wrote:
> 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.
>

Sure, but the installer aligns to the reported "stripe size". For AF 
disks like your SSD, the kernel reports the right thing in the stripe size.

Where in the forum thread does it show an issue? The only thing I see is 
some gpart output from a 10K spinning SAS disk, which almost certainly 
has 512-byte physical sectors.
-Nathan