df shows wrong disk size

[Ross Boylan <rossboylan@stanfordalumni.org>]

df says my volume is 3G, but everything else says it's 4G.  What's
going on and how can I correct it?

This question concerns the total reported space, not the free space.

The volume is an LVM logical volume on buster with an ext4 file
system.  I originally mistakenly created it as 4TB in size.
Then I took it offline, resized the file system to 3G, resized the
logical volume to 4G, and  then auto-resized (that is, ran resize2fs
without specifying an explicit size) the file system to 4G.  When df
showed the size as 3G I thought it might be temporary, but it it
reports the same value after reboot.

(If you're wondering: I resized to 3G first out of concern that the
file system requires a slightly larger "partition" than its own size,
and I didn't want to risk cutting off the end of the file system.)

I thought there might have been a huge amount of reserved space or
journal from the original 4TB size, but the values in dumpe2fs appear
normal to me.

Running buster.

Thanks.
Ross

# df -h /var/local/cache/
Filesystem                  Size  Used Avail Use% Mounted on
/dev/mapper/vgbarley-cache  3.0G  721M  2.1G  26% /var/local/cache
root@barley:~/tempserver/root# lvs vgbarley
  LV      VG       Attr       LSize   Pool Origin Data%  Meta%  Move
Log Cpy%Sync Convert
  cache   vgbarley -wi-ao----   4.00g
## etc
# resize2fs /dev/vgbarley/cache
resize2fs 1.44.5 (15-Dec-2018)
The filesystem is already 1048576 (4k) blocks long.  Nothing to do!
# So both LVM and e2fs utilities see 4G , even thouogh df reports 3G

# somewhat later
# dumpe2fs -h /dev/vgbarley/cache
dumpe2fs 1.44.5 (15-Dec-2018)
Filesystem volume name:   <none>
Last mounted on:          /var/local/cache
Filesystem UUID:          0601d7dc-2efe-46c7-9cac-205a761b70ef
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index
filetype needs_recovery extent 64bit flex_bg sparse_super large_file
huge_file dir_nlink extra_isize metadata_csum
Filesystem flags:         signed_directory_hash
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              131072
Block count:              1048576
Reserved block count:     52428
Free blocks:              621488
Free inodes:              122857
First block:              0
Block size:               4096
Fragment size:            4096
Group descriptor size:    64
Reserved GDT blocks:      1024
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         4096
Inode blocks per group:   256
Flex block group size:    16
Filesystem created:       Mon May 27 11:54:50 2019
Last mount time:          Thu May 30 17:06:02 2019
Last write time:          Thu May 30 17:06:02 2019
Mount count:              2
Maximum mount count:      -1
Last checked:             Mon May 27 14:17:18 2019
Check interval:           0 (<none>)
Lifetime writes:          35 GB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:              256
Required extra isize:     32
Desired extra isize:      32
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      24162063-f4a6-4420-b79b-3ad4f9b71ab7
Journal backup:           inode blocks
Checksum type:            crc32c
Checksum:                 0x48ff013b
Journal features:         journal_64bit journal_checksum_v3
Journal size:             1024M
Journal length:           262144
Journal sequence:         0x000005be
Journal start:            1
Journal checksum type:    crc32c
Journal checksum:         0xb7b54059