When running an ls -la command in a particular directory, you will generally see output like the following, obviously dependent on where you run it:

Logapp root:/loglogic/data 0$ ls -la
total 188800
drwxr-xr-x 37 mysql  users      4096 Sep 12 14:59 .
drwxrwxr-x 35 root   root       4096 Sep 12 14:57 ..
drwxr-xr-x  2 logapp root       4096 Aug 30  2018 archive
-rw-r-----  1 mysql  users        56 Aug 29 11:15 auto.cnf
drwxr-xr-x  6 logapp root       4096 Aug 30  2018 backup_preparation
drwxr-xr-x  2 logapp logapp     4096 Aug 30  2018 bkup
-rw-------  1 mysql  users      1680 Aug 30  2018 ca-key.pem
-rw-r--r--  1 mysql  users      1075 Aug 30  2018 ca.pem
-rw-r--r--  1 mysql  users      1079 Aug 30  2018 client-cert.pem
-rw-------  1 mysql  users      1676 Aug 30  2018 client-key.pem
drwxr-xr-x  2 root   root       4096 Aug 30  2018 client_queue
drwxr-x---  2 mysql  users      4096 Aug 30  2018 correlation
...
...
...
-rw-r--r--  1 root   root         10 Aug 30  2018 ipaddress
drwxr-x---  2 mysql  users     12288 Sep 20 00:02 ll_auth_logs
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_cached_results
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_files
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_files_in
drwxr-x---  2 mysql  users     32768 Aug 30  2018 ll_firewall_logs
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_ids_logs
drwxr-x---  2 mysql  users     16384 Sep 20 02:30 ll_misc_logs
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_postupgrade
drwxr-x---  2 mysql  users     40960 Sep 20 00:00 ll_stats
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_temp_results
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_vpn_logs
drwxr-x---  2 mysql  users      4096 Aug 30  2018 ll_www_logs
drwxr-x---  2 mysql  users     20480 Sep 20 14:41 logappconfig
drwxr-x---  2 mysql  users      4096 Aug 30  2018 logapplogu
-rw-r-----  1 mysql  users         6 Sep 12 14:59 logappmysqld.pid
drwxr-x---  2 mysql  users     69632 Sep 20 16:29 logapprtrpt

The highlighted entries are directories and, as you can see, the majority have a listed size of 4096 bytes, or 4KB. Why is this?
 

On an ext3 or ext4 filesystem, the default inode size is 256 bytes, whilst the default block size is 4096 bytes. A directory is just a special file which contains an array of filenames and the inodes they reference, an inode being a structure on the disk that contains file attributes, metadata, and so on.  When a directory is created, all it contains is one filename (actually the directory name itself), pointing to one inode (that of the directory). That inode points to a single data block, which is the minimum space that can be allocated which, as we have seen, is 4096 bytes. This is why most directories show a size of 4096 bytes when an ls -la is run - they do not contain enough data structures to require more space than the minimum amount that's allocated.

What you can see from the ls -la output above is that some directories are showing as larger than 4096 bytes, e.g.:

drwxr-x---  2 mysql  users     32768 Aug 30  2018 ll_firewall_logs
drwxr-x---  2 mysql  users     16384 Sep 20 02:30 ll_misc_logs
drwxr-x---  2 mysql  users     40960 Sep 20 00:00 ll_stats
drwxr-x---  2 mysql  users     69632 Sep 20 16:29 logapprtrpt

What this shows is that the data structure referenced inside them requires more space than the minimum size can contain.  Note as well that all the size values are multiples of the minimum block size (4096 bytes) as these are the smallest chunks that can be allocated. Checking the size of directories can be a useful troubleshooting tool, especially if you have a baseline to compare against. For example, we have often seen that file collection problems can cause the size of ll_files to grow by orders of magnitude. If we are aware of the size that it SHOULD be, it is easy to diagnose that this is an area we should focus on.

 

This article explains why the vast majority of directories show as being 4KB in size on the filesystem.