Dangerously dedicated mode with FreeBSD 10.1

[Nathan Whitehorn]

On 11/21/14 14:32, Warren Block wrote:
> On Fri, 21 Nov 2014, Nathan Whitehorn wrote:
>
>>
>> On 11/21/14 07:26, Warren Block wrote:
>>> On Fri, 21 Nov 2014, Rostislav Krasny wrote:
>>>
>>>> Hi,
>>>>
>>>> I've a server with FreeBSD 7.4-STABLE that uses two phisical disks in
>>>> a so called "dangerously dedicated mode". There is no other operating
>>>> system and no plan to install anything else but FreeBSD. So in my case
>>>> this is not dangerous mode at all.
>>>>
>>>> I want to upgrade it by installing FreeBSD 10.1 from scratch and I
>>>> want to use the dedicated disk mode again. How could I do that?
>>>>
>>>> If I understand it right the new bsdinstall(8) doesn't support the
>>>> dedicated disk mode, the old sysinstall(8) is already dead and the
>>>> only solution is a manual disk partitioning from shell. The 2.6.5.
>>>> Shell Mode Partitioning section of the Handbook is very terse about
>>>> that.
>>>
>>> If you are determined, it should be possible to select a 
>>> bsdlabel-only format with the Manual partitioning option in the 
>>> menus, or enter Shell mode on startup and create it with gpart or 
>>> even bsdlabel.  That said, I can't think of any advantages of using 
>>> a bare bsdlable at all.  With 10.1, GPT is available, supports large 
>>> disks, and is easily alignable.*
>>
>> Right, just select "BSD" as the partition type.
>>
>>> *: although it is reported that bsdinstall for 10.1 does not 
>>> automatically do 4K alignment. But at least there are advantages to 
>>> using it as a partition scheme.
>>
>> 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.
-Nathan