On Wed, Mar 27, 2013 at 4:22 PM, Marc MERLIN <m...@merlins.org> wrote: > On Wed, Mar 27, 2013 at 04:12:27PM -0500, Mitch Harder wrote: >> On Wed, Mar 27, 2013 at 11:53 AM, Marc MERLIN <m...@merlins.org> wrote: >> > >> > Is my feeling of slower boot wrong, or is zlib also noticeably slower than >> > lzo to read and decompress? >> > >> >> Lzo compression should be faster in every aspect than zlib, especially >> for reading. >> >> But having said that, btrfs won't recompress any existing files just >> because you switch your mount option from lzo to zlib. Only newly >> written files will be zlib, and btrfs will leave the lzo-compressed >> files alone unless they are re-written, or you expressly recompress >> them using the defrag tool. > > That was my intent at the time, I thought that zlib decompression was about > as fast as lzo, so it would have been good that most my files stayed > compressed as zlib. > Turns out I was wrong :) > >> If you were to take a snapshot of your root partition, and reboot to >> the snapshot as the new root with zlib compression, you could make >> some side-by-side comparisons of boot time to clarify your >> impressions. > > Fair point. By that, you mean degrag all my files somehow (recompressing as > lzo, and doubling the size of my rootfs)? > > Also, I was re-reading ssd vs nossd: > https://btrfs.wiki.kernel.org/index.php/Mount_options > isn't clear whether these are read/write ordering optimizations, or > filesystem layout optimization (i.e. you'd have to recreate the entire FS, > and rewrite everything). > > http://www.phoronix.com/scan.php?page=article&item=btrfs_ssd_mode&num=1 > says 'However, unless disabling the write cache for the drive, the SSD mode > does not necessarily mean better performance. In fact, as our results are > about to show, the quantitative disk performance can drop greatly in the SSD > mode when the write cache remains enabled' > But that's from 2009, so not very relevant to today. > > Do you happen to know more than me on this? >
I'm sorry, I have no experience with the ssd mount option. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
