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==Do LVM and filesystem resize in single step (Preferred)==
Since various commands such as lvresize / resize2fs may use different units KB (1000) instead of KiB (1024), it is better to perform both filesystem and LVM resize using a single command and avoid any issues.  In that case the reduction can be achieved via:
# Validate current usage and free space.  We can reduce filesystem to value less than current used space.
#:<pre>
#:: df -h
#:</pre>
# Umount the filesystem
#:<pre>
#:: umount <device>
#:</pre>
# Check the filesystem for errors before resizing
#:<pre>
#:: fsck -f <device>
#:</pre>
# Finally resize both LVM and Ext partition using:
#:<pre>
#:: lvresize --resizefs --size <desired-final-size> <device>
#:</pre>
#: Here we can specify size as 200g (200 GiB) or 200G (200GB) based on requirement 
# (Optionally) Check the filesystem again for errors after resizing
#:<pre>
#:: fsck -f <device>
#:</pre>


Refer
* https://www.systutorials.com/shrinking-a-ext4-file-system-on-lvm-in-linux/



==Running LVM and ext resize separately (Not preferred)==
In case size of ext partition (ext2-4) needs to be reduced, it can be done as follows:
# Check the occupied and free space on partition:
#:<pre>
#:: df -h
#:</pre>
#: Ensure that we do not try to resize the partition to value less than free space.  Ideally even after resizing try to keep usage at 80% or less.
# First umount the partition
#:<pre>
#:: umount /dev/mapper/vg1-lv1
#:</pre>
# Look at existing block count and block size before resizing using:
#:<pre>
#:: dumpe2fs -h /dev/mapper/vg1-lv1 | grep -i block
#:</pre>
#: and look for values of 'Block count' and 'Block size'.  After resize the 'Block size' would remain same but 'Block count' should decrease.
# Then ensure that filesystem is healthy using:
#:<pre>
#:: fsck -f /dev/mapper/vg1-lv1
#:</pre>
# We can use resize2fs to resize filesystem to desired size using:
#:<pre>
#:: resize2fs /dev/mapper/vg1-lv1 80G
#:</pre>
#: Here instead of 80GB specify desired size.  Also note the point mentioned above related to used and free space.  Try to keep at least 20% free space even after resizing.  Hence if we are resizing to 80GB.  The partition should have data about 63GB or less.
#: resize2fs has -M option to minimize the size of partition based on existing data.
# Once filesystem is resized, its new size can be checked using:
#:<pre>
#:: dumpe2fs -h /dev/mapper/vg1-lv1 | grep -i block
#:</pre>
#: and look for updated values of 'Block count' and 'Block size'. 
# We can now resize the physical partition and make it smaller via fdisk / parted / lvm.  The partition size should be at least 'Block count' x 'Block size' bytes long.  Ideally keep some buffer for suprises.  We can again do resize2fs /dev/mapper/vg1-lv1 to extend / expand the partition to match the partition size.
# Optionally run "fsck -f" once again before remounting

Refer:
* http://www.microhowto.info/howto/reduce_the_size_of_an_ext2_ext3_or_ext4_filesystem.html



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