On Wed, Nov 04, 2015 at 09:10:42PM +0000, OmegaPhil wrote: > Back in September I noticed that 'sudo du -chs /mnt/storage-1' reported > 887GB used and 'df -h' 920GB for this particular volume - I went on > #btrfs for any suggestions, and balancing + defraging made no > difference. It had no subvolumes/snapshots etc, I basically used it like > a checksumed ext4fs. > > Since the volume was converted from ext4, I redid it from scratch (so > made with kernel v4.1.3 or v4.1.6 on this Debian Testing machine), and > the problem went away. > > After a couple of months, df reports 907GB used, whereas du says 884GB - > I currently have 8 large (1-5.5TB volumes) btrfs volumes in use, > storage-1 is the only SSD volume and the only one with this problem. > > No balancing or defraging this time, it didn't make a difference before > and this is a relatively new volume. > > Are there any sysadmin-level ways I can account for the ~23GB lost space?
There's an issue where replacing blocks in the middle of an existing extent won't split the extent, and thus the "old" blocks aren't freed up, because they're held by the original extent (even though not actually referenced by any existing file). This might be what you're seeing. I'm not sure how to confirm this theory, or what to do about it if it's true. (Defrag the file? Copy it elsewhere? Other?) Two other cases for df > du are orphaned files, although 23 GiB of orphans is large; and missing out the dot-files in the directory that du is run from (if doing, say, "du *" rather than "du ."). I've been bitten by both of those in the past. Hugo. > Thanks for any help. > > ========================================================= > > $ uname -a > > Linux omega1 4.2.0-1-amd64 #1 SMP Debian 4.2.5-1 (2015-10-27) x86_64 > GNU/Linux > > $ btrfs --version > > btrfs-progs v4.2.2 > > $ sudo btrfs fi usage /mnt/storage-1 > > Overall: > Device size: 953.87GiB > Device allocated: 932.04GiB > Device unallocated: 21.83GiB > Device missing: 0.00B > Used: 906.10GiB > Free (estimated): 45.35GiB (min: 34.43GiB) > Data ratio: 1.00 > Metadata ratio: 2.00 > Global reserve: 512.00MiB (used: 0.00B) > > Data,single: Size:925.01GiB, Used:901.50GiB > /dev/sdb 925.01GiB > > Metadata,single: Size:8.00MiB, Used:0.00B > /dev/sdb 8.00MiB > > Metadata,DUP: Size:3.50GiB, Used:2.30GiB > /dev/sdb 7.00GiB > > System,single: Size:4.00MiB, Used:0.00B > /dev/sdb 4.00MiB > > System,DUP: Size:8.00MiB, Used:128.00KiB > /dev/sdb 16.00MiB > > Unallocated: > /dev/sdb 21.83GiB > > $ sudo btrfs-show-super /dev/sdb > > superblock: bytenr=65536, device=/dev/sdb > --------------------------------------------------------- > csum 0x7f6b70be [match] > bytenr 65536 > flags 0x1 > ( WRITTEN ) > magic _BHRfS_M [match] > fsid 27430475-c49a-4e3f-8f8d-be5c14be59db > label storage-1 > generation 114344 > root 683413471232 > sys_array_size 226 > chunk_root_generation 114251 > root_level 1 > chunk_root 21004288 > chunk_root_level 1 > log_root 683413979136 > log_root_transid 0 > log_root_level 0 > total_bytes 1024209543168 > bytes_used 971565568000 > sectorsize 4096 > nodesize 16384 > leafsize 16384 > stripesize 4096 > root_dir 6 > num_devices 1 > compat_flags 0x0 > compat_ro_flags 0x0 > incompat_flags 0x161 > ( MIXED_BACKREF | > BIG_METADATA | > EXTENDED_IREF | > SKINNY_METADATA ) > csum_type 0 > csum_size 4 > cache_generation 114344 > uuid_tree_generation 114344 > dev_item.uuid c6b32341-6300-4f21-8c3b-3d7d458c3668 > dev_item.fsid 27430475-c49a-4e3f-8f8d-be5c14be59db [match] > dev_item.type 0 > dev_item.total_bytes 1024209543168 > dev_item.bytes_used 1000765128704 > dev_item.io_align 4096 > dev_item.io_width 4096 > dev_item.sector_size 4096 > dev_item.devid 1 > dev_item.dev_group 0 > dev_item.seek_speed 0 > dev_item.bandwidth 0 > dev_item.generation 0 > > ========================================================= > > dmesg contains a lot of information which is superfluous to btrfs and > personal, I can filter on a regex and report if necessary. > -- Hugo Mills | There are three things you should never see being hugo@... carfax.org.uk | made: laws, standards, and sausages. http://carfax.org.uk/ | PGP: E2AB1DE4 |
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