On Aug 31, 2014 1:54 AM, "Jakub Klinkovský" <j.l.k@xxxxxxx> wrote: > > On 30.08.14 at 21:58, Temlin Olivér wrote: > > > Whenever I start my laptop up, /home takes ~17-19 seconds to mount > > You can always use x-systemd.automount in fstab, which delays the mount to > > the first access (ie. non-root login), or mask home.mount to be > > non-blocking (oneshot), so it runs parallel with the login manager and > > password input. > > Slow mount times are usually caused by large log trees and fragmented > > metadata. Try the autodefrag mount option and btrfs fi defrag -clzo -t 2M > > -r /home (defragment files over 2M in size, recompress with lzo, > > recursively), btrfs balance start /home (and wait for btrfs-endio-wri to > > calm down or check with balance status, this takes some time) > > If those don't help enough, try checking (but not repairing) the device > > with btrfsck, and, if it's clean, clear the logs with btrfs-zero-image > > after backing up the metadata with btrfs-image (consult the btrfs mailing > > list or IRC first, I am not an expert in this). > > > > > Running df -h on my system, I get: > > > /dev/sda5 422G 364G 53G 88% /home > > Please use btrfs filesystem df (fi df for short), as it will show you both > > the data and metadata allocation with better reflection on actual free data > > space. > > > > Point is, the allocation on B* trees can only be measured by a full tree > > traversal (as your du try shows the true data usage, but misses > > fragmentation), but btrfs usage is even more complicated. Authors suggest > > that a device never be filled over 75% to avoid metadata fragmentation, but > > by having larger files this can truly be about 95%. > > > > Sorry for the long text, but I belive this helps in better understanding. > > > > --Oliver Temlin > > Also note that `du` does not account for Copy-on-Write, so it could actually > show higher value than what `btrfs fi df` reports. Thank you for all the help. In the end, I decided to get rid of about 50G of files I didn't need (transferred them to an NTFS disk, where I saw the size), and that increased the amount of free space I had, paradoxically, by more than 60 gigs. I then defragmented the system and ran xdiskusage after that. The /home/(permission denied) bit had shrunk from 48 gigs to 30 gigs. I'm running the balance command as I type this mail to see if I manage to free up any more space. Again, another weird thing is that the btrfs filesystem df /home showed 398 gigs to space in home before all this, and now it shows 402 gigs. Something is definitely up. I'll probably open up their IRC channel and talk if someone knowledgeable happens to be online. @Jakub Klinkovsky - In my case, du showed a lower value than btrfs fi df /home. Thanks, Savya
