Allowing arbitrary MBR slice alignment

[Ulf Lilleengen]

On Friday 14. February 2014 09.24.34 Warren Block wrote:
> The Problem
> 
> More and more disk devices have native 4K blocks.  The ability to align
> MBR slices to arbitrary values is consequently becoming more important.
> Misaligned filesystems might read or write at less than half the speed
> of aligned filesystems on the same disk.
> 
> Microsoft recognized this problem, and at least since the release of
> Vista in 2007, MBR-formatted disks created by Microsoft operating
> systems have started the first or main filesystem slice at block 2048
> (1M).  Despite the official standard for MBR alignment to CHS values,
> this second non-CHS but 4K-aligned de facto standard has become
> extremely common.
*snip*
> Suggested Solution
> 
> gpart(8) should be allowed to override the CHS rounding with -a and -b
> values when creating MBR slices.  If CHS rounding occurs when the
> options are not given, gpart(8) should give a warning that default
> values were used to avoid surprising the user.
> 
> The warning is really secondary.  Primarily and pragmatically, gpart(8)
> needs the ability to create MBR slices with arbitrary alignment so
> FreeBSD can deal gracefully with modern storage hardware.
> 

IMHO, 4k alignment should be default in freebsd as well, unless there are some 
actual disadvantages for the users. I think the majority of users would like 
good performance. But allowing to override it is a good start :)  

Ulf