Where is my disk space?

For example take my disk space in my  .platform.app.yaml  as below

                    disk: 214528  NOTE: This is in MB
 

I should get 209 GB because 214528/1024 = 209.5 GB.

But I get only 207GB when I check using 

      df -h /mnt 
     /dev/mapper/xxxx  207G  205G  1.7G 100% /mnt

So where did my 2.5GB go?

Note that file system information is complex. It needs to store information about files metadata, journal data, super blocks, block data, block groups and more inode information.  It also takes a backup and that needs to be stored in super block too. So all these things takes spaces depending on the disk size and files. 

Even in default  ext3/ext4 file system the default served block percentage is 5%. 

Ref:  https://linux.die.net/man/8/mkfs.ext4

In our case it appears (no concrete evidence that it is indeed 1.5% but it's a very rough math as it's not straight forward to calculate the block size)

214528 * 1.5% = 3217.92 MB 

There for 214528 − 3217 =  211311 MB

Upon division  211311/1024  =  207GB (rounded) we get 207GB.

Hope that explains where the missing disk space is going.