Re: File system blocks alignment

On Fri, 01.01.2010 at 22:47:12 +0000, Poul-Henning Kamp wrote:
> In message <201001012153.44349.pieter_at_degoeje.nl>, Pieter de Goeje writes:
> 
> >That yielded some pretty spectacular results. [...]
> >
> >Performance for restore was abysmal in the unaligned case, easily being 10 
> >times slower than aligned restore. Newfs was about 5 times as slow.
> 
> That is what I expected, only I didn't expect a factor 14 in performance.
> 
> I'm not surprised that newfs and restore take the biggest hits in that
> test, those are the hard ones, seen from the disk drive, all the read
> only work can be cached and "covered up" that way.
> 
> Ideally, newfs/UFS should do a quick test to look for any obvious
> boundaries, and DTRT, a nice little task for somebody :-)

Indeed, but newfs is only one small part of the puzzle. Think about
zpools and, more importantly swap partitions. Sysinstall, fdisk, gpart
and bsdlabel should all display some fat warning if partition/label
alignment is not, say at 256kB (a common stripe size, right?) and also
automatically generate that offset if the user uses automatic settings.

But then again, this is all wishful thinking from a users perspective :)

Regards,
Uli