Am Sonntag, 26. August 2012, 14:49:08 schrieb Alex Schuster: > Volker Armin Hemmann writes: > > Am Sonntag, 26. August 2012, 13:41:09 schrieb Alex Schuster: > >> Frank Steinmetzger writes: > >>> 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. > > Yes, I know that. But why exactly does it help to align a partition to > the erasable block size? I don't get it. Why isn't it sufficient to > align to the usual 4K block size, so that a block never spans over two > erasable blocks?
well, for one, there are lots of ssd which have 8k pages. Not 4k. -- #163933
