Volume show different sizes in CentOS 7

Question

I hope you and your dears are very well.

I'm facing a issue which I cannot understand the root cause.

I have a VM with CentOS 7 64 bits. This VM has the following partitions:

Filesystem           Size  Used Avail Use% Mounted on
/dev/mapper/cl-root  1.1T  1.1T  3.1G 100% /
devtmpfs             126G     0  126G   0% /dev
tmpfs                126G     0  126G   0% /dev/shm
tmpfs                126G  4.1G  122G   4% /run
tmpfs                126G     0  126G   0% /sys/fs/cgroup
/dev/sda3            239M  147M   76M  66% /boot
/dev/mapper/cl-tmp   190M  1.6M  175M   1% /tmp
tmpfs                 26G     0   26G   0% /run/user/0

In the mount point / (root), as you can see I have just 3.1 GB available of a volume total size 1.1 TB.

I tried to identify if there is some delete file locked by some process, but this is not the case:

# ls -l /proc/*/fd/* | grep deleted
ls: cannot access /proc/20484/fd/255: No such file or directory
ls: cannot access /proc/20484/fd/3: No such file or directory
ls: cannot access /proc/self/fd/255: No such file or directory
ls: cannot access /proc/self/fd/3: No such file or directory

Using parted, I find that this partition has the following size:

#parted /dev/cl/root
GNU Parted 3.1
Using /dev/dm-0
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print free
Model: Linux device-mapper (linear) (dm)
Disk /dev/dm-0: 1197GB
Sector size (logical/physical): 512B/512B
Partition Table: loop
Disk Flags:
Number  Start  End     Size    File system  Flags
1   0.00B  1197GB  1197GB  ext4

Using lvdisplay to check the logical volume, I have:

# lvdisplay /dev/mapper/cl-root
  --- Logical volume ---
  LV Path                /dev/cl/root
  LV Name                root
  VG Name                cl
  LV UUID                hwPnR8-7VX2-DNjb-HUjU-Cbai-Rl37-txslGH
  LV Write Access        read/write
  LV Creation host, time computer-node-07, 2018-10-17 13:59:48 -0300
  LV Status              available
  #open                  1
  LV Size                1.09 TiB
  Current LE             285364
  Segments               10
  Allocation             inherit
  Read ahead sectors     auto
  -currently set to     256
  Block device           253:0

Now, when I get the volume size using du, I had the following output:

du -csh --block-size=1G /Mb
du: cannot access ‘/proc/173159/task/173159/fd/3’: No such file or directory
du: cannot access ‘/proc/173159/task/173159/fdinfo/3’: No such file or directory
du: cannot access ‘/proc/173159/fd/4’: No such file or directory
du: cannot access ‘/proc/173159/fdinfo/4’: No such file or directory
1049
1049    total

I also tried to find whether there is a available space in the Volume Group, but I don't have:

# vgdisplay -v cl|grep Free
  Free  PE / Size       0 / 0
  Total PE / Free PE    285414 / 0

Could you help me to understand this situation?

Thanks. Cardoso

Answer 1

The reported size from the tools seems to be the same. You have a 1.09 TiB root logical volume, df output is rounded and parted shows 1197 GB which is 1.09 TiB.

The "missing" free space is the filesystem reserved space. It's by default 5 % on ext4. You can check number of reserved blocks in dumpe2fs. You can change the reserve size using tune2fs -m <size> <device>, see this question for more details about reserved space on ext4.