Re: [gentoo-user] SSD performance tweaking

[Volker Armin Hemmann <volkerarmin@googlemail.com>]

Am Sonntag, 26. August 2012, 13:41:09 schrieb Alex Schuster:
> Frank Steinmetzger writes:
>  > On Thu, Aug 23, 2012 at 12:15:20PM +0200, Alex Schuster wrote:
> >> The size of an erasable block of SSDs is even larger, usually 512K, it
> >> would be best to align to that, too. A partition offset of 512K or 1M
> >> would avoid this.
> > 
> > Unless the filesystem knows this and starts bigger files at those 512 k
> > boundaries (so really only one erase cycle is needed for files <=512 k),
> > isn't this fairly superfluous?
> 
> Yes, I think it is. When you search for SSD alignment, you read about
> this alignment all the time, even on the German Wikipedia, and many
> resources say that this can have a big impact on performance. But I
> could not find a real explanation at all.
> 
> Besides that, it's not so easy to do the alignment, at least when using
> LVM. I read that LVM adds 192K header information, so even if you align
> the partition start to an erasable block size of 512K, the actual
> content is not aligned. See [*] for information how to overcome this.
> That is, if you believe the alignment to erasable blocks is important,
> personally I do not know what to think now. It wouldn't hurt, so why not
> apply it, but it seems like snake oil to me now.
> 
> 	Wonko
> 
> http://tytso.livejournal.com/2009/02/20/

because erasing is slow. You can not overwrite data on a ssd. you have to 
erase first, then reprogramm. Also, erasing shortens lifetime. 

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