This. From the Btfrs Gotchas page: Files with a lot of random writes can become heavily fragmented (10000+ > extents) causing thrashing on HDDs and excessive multi-second spikes of CPU > load on systems with an SSD or large amount a RAM. > > - On servers and workstations this affects databases and virtual > machine images. > - The nodatacow mount option > <https://btrfs.wiki.kernel.org/index.php/Mount_options> may be of > use here, with associated gotchas. > - On desktops this primarily affects application databases (including > Firefox and Chromium profiles, GNOME Zeitgeist, Ubuntu Desktop Couch, > Banshee, and Evolution's datastore.) > - Workarounds include manually defragmenting your home directory > using btrfs fi defragment. Auto-defragment (mount option autodefrag) > should > solve this problem in 3.0. > - Symptoms include btrfs-transacti and btrfs-endio-wri taking up a lot > of CPU time (in spikes, possibly triggered by syncs). You can use filefrag > to locate heavily fragmented files (may not work correctly with > compression). > > On Wed, Jul 31, 2019 at 5:50 AM Mart van de Wege <mvdw...@gmail.com> wrote:
> Stefan Monnier <monn...@iro.umontreal.ca> writes: > > >> Is it safe to use autodefrag for my use case? > > > > It sounds like it might be "safe" (the text doesn't actually say it's > > unsafe, but just that it has downsides). > > > > I do wonder why you'd want to do that, tho. Fragmentation is typically > > something that clueless Windows users worry about > > No. Fragmentation is an issue with all copy-on-write filesystems > (including ZFS, which avoids periodic defrag by keeping an enormous > amount of information in memory and doing defrag on the fly on that). > > Mart > > -- > "We will need a longer wall when the revolution comes." > --- AJS, quoting an uncertain source. > >
