damn you stumped me again with that question.
when you run mkfs.filesystem_extn viz. mkfs.ext2 or mkfs.ext3 and pass the switch -v you will see mkfs will allocate some blocks for the inode tables. and inode tables is where the file system is indexed. inode table is like house door number which tells the io where to seek the file. thus if your partition size is 512 MiB? and you are trying to have 512 MiB as space for that file system? then either set the size/resize of that partition to 550+ MiB. even if you use jffs which is nice when space is a pinch else try ext2 and set the block size normal which is 512 or ext3 with block size 1k, you will still need to sacrifice some space for the creation of the inode tables.
you really got me stumped. because you can never have the cake and eat it.
thus if you think you use fdisk and make a 512 mb partition and also want to have 512 mb space? be my guest.


aaru you became my guest:
#mke2fs -m reserved-blocks-percentage /dev/hda1

Note:

refer man page of mke2fs
i will buy you some beer. please also run dumpfs -v and debugfs -v and show me how you got 512 MB space of a 512 MB space parition against that /dev/drive_map_device_partition_number.