svn commit: r304142 - head/usr.sbin/bsdinstall/partedit

[Slawa Olhovchenkov]

On Wed, Aug 17, 2016 at 07:36:00AM -0700, Nathan Whitehorn wrote:

> > Your contention that the installer does not make policy decisions is
> > equally spurious.  The installer makes many policy decisions, including
> > the disk layout, the size of the swap partition, the name of the pool,
> > the use of boot environments (which I dislike but am not allowed to
> > override), the number of filesets and their mountpoints (which I also
> > dislike and am not allowed to override either), etc.  The Unix
> > philosophy is to push such decisions up the stack, not down.  The
> > decision to align partitions on 4096-byte boundaries because we're not
> > sure of the correct number but know for a fact that using a smaller
> > number can have a huge impact on performance is the installer's to make.
> 
> Those are all things that the operating system does not have defaults 
> for: there are no tools like, say, gpart or newfs that layout disks in 
> any even vaguely automated way, and so no tools that would ever have 
> defaults for, say, the size of a swap partition except for the 
> installer. As such, the defaults are quite properly in the installer. 
> This is quite different: there are many tools that care about disk 
> alignment (say, gpart) and, by default, use the GEOM stripesize. The 
> installer is, after this patch, overriding what was meant to be a 
> system-wide default.
> 
> My concern is that pushing this into the installer means that newfs, 
> zfs, gpart, etc., which all look at the GEOM stripesize for preferred 
> alignment, will still have suboptimal behavior on systems affected by 
> your patch. If we identified which drivers are reporting the wrong 
> alignment, we could fix the whole system at a go by changing it there. 
> As it is, we now have inconsistent default behavior for partitions 
> between tools (the installer and sade will now use a different alignment 
> than gpart on whatever systems you were trying to fix here) and between 
> pre- and post-installation environments.

In long term, prefered aligment is forsing 4k (or may be more):
install system on 512b [mirror] disk aligment now may be need required replace
disk to 4k aligment. For more flexsible in future now best chois is 4k
or more.