geli overhead?

[mhca12]

Is there some overhead associated with the geli setup as
described earlier?

$ df -h
Filesystem         Size    Used   Avail Capacity  Mounted on
/dev/ada0p3.eli    127G    6.9G    119G     5%    /
devfs              1.0k    1.0k      0B   100%    /dev
/dev/gpt/boot      991M    339M    642M    35%    /bootdir
$ gpart show
=>       34  312581741  ada0  GPT  (149G)
         34        128     1  freebsd-boot  (64k)
        162    2097152     2  freebsd-ufs  (1.0G)
    2097314  310484461     3  freebsd-ufs  (148G)

Where did 21G from the 148G go?

As suggested in dan.me.uk geli install guide I used geli init -a HMAC/SHA256
and also ran dd if=/dev/zero of=/dev/gpt/enc.eli across the eli volume.