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Good morning, I've a "little" problem in my backup machine. It can not be able to do the backups, because it detect 96% space used. But it is not true.

I launched some commands on the physical machine, here I give you the outputs.

ubuntu@BACKUP:~$ sudo df -h
Filesystem                           Size  Used Avail Use% Mounted on
udev                                 992M     0  992M   0% /dev
tmpfs                                200M   21M  180M  11% /run
/dev/xvda1                            20G  4.8G   15G  25% /
tmpfs                               1000M     0 1000M   0% /dev/shm
tmpfs                                5.0M     0  5.0M   0% /run/lock
tmpfs                               1000M     0 1000M   0% /sys/fs/cgroup
/dev/mapper/vg_data-lv_data_backup   640G  580G   30G  96% /data/backup
/dev/mapper/vg_data-lv_data_archive  640G   49G  559G   9% /mnt/lv_data_archive
tmpfs                                200M     0  200M   0% /run/user/1000

As you can see, in /dev/mapper/vg_data-lv_data_backup there are 30GB disappeared. I know it is an ext4 partition and it reserves 5% space for root commands. But it doesn't justify this wrong space...

Here other commands:

root@BACKUP:/data# du -h -d1 /data/backup
16K /data/backup/lost+found
531G    /data/backup/BackupPC
50G /data/backup/DumpDB
580G    /data/backup

ubuntu@BACKUP:~$ sudo lsof +L1 | numfmt --field=7 --to=iec --invalid='ignore'
    COMMAND    PID     USER  FD   TYPE DEVICE SIZE/OFF NLINK  NODE NAME
    systemd-j  388     root txt    REG  202,1     319K     0 52456 /lib/systemd/systemd-journald (deleted)
    dhclient  1010     root txt    REG  202,1     476K     0  4269 /sbin/dhclient (deleted)
    lxcfs     1202     root txt    REG  202,1      19K     0 24454 /usr/bin/lxcfs (deleted)
    systemd-l 1233     root txt    REG  202,1     605K     0 52482 /lib/systemd/systemd-logind (deleted)
    agetty    1476     root txt    REG  202,1      44K     0  4308 /sbin/agetty (deleted)
    agetty    1482     root txt    REG  202,1      44K     0  4308 /sbin/agetty (deleted)
    BackupPC  1625 backuppc txt    REG  202,1     1.9M     0  6550 /usr/bin/perl (deleted)

root@BACKUP:/data# dumpe2fs -h /dev/mapper/vg_data-lv_data_backup 
dumpe2fs 1.42.13 (17-May-2015)
Filesystem volume name:   <none>
Last mounted on:          /data/backup
Filesystem UUID:          8f2689b8-6ed0-47d2-833c-904097eb6a34
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
Filesystem flags:         signed_directory_hash 
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              42598400
Block count:              170393600
Reserved block count:     7869498
Free blocks:              57647530
Free inodes:              40094191
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      983
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Flex block group size:    16
Filesystem created:       Tue Aug 22 12:04:28 2017
Last mount time:          Fri Dec 15 12:20:05 2017
Last write time:          Fri Dec 15 12:20:05 2017
Mount count:              16
Maximum mount count:      -1
Last checked:             Tue Aug 22 12:04:28 2017
Check interval:           0 (<none>)
Lifetime writes:          5450 GB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:           256
Required extra isize:     28
Desired extra isize:      28
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      fd48ebc6-99be-468a-8c2d-3aa600ce2412
Journal backup:           inode blocks
Journal features:         journal_incompat_revoke
Journal size:             128M
Journal length:           32768
Journal sequence:         0x00011b23
Journal start:            30397

Thank you

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1 Answer 1

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As you wrote, ext4 reserves 5% of the space for root. Not for root "commands", but for files. 5% of 640 Gb are 32 Gb, which modulo rounding errors is the amount of disk space you are looking for. These Gb are physically on disk, but not available to normal users, hence not shown in the "available" column of df.

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