Linux – rsync fails – No space left on device (28)

I want to backup ~5 GB of photos from one server to another.

Rsync downloads about 80% of all files and then synchronization fails:

rsync: write failed on "/var/www/sync/3655467597474553464543.jpg": No space left on device (28)
rsync error: error in file IO (code 11) at receiver.c(322) [receiver=3.0.9]
rsync: connection unexpectedly closed (596 bytes received so far) [generator]
rsync error: error in rsync protocol data stream (code 12) at io.c(605) [generator=3.0.9]

df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs           20G   15G  3.7G  80% /
/dev/root        20G   15G  3.7G  80% /
devtmpfs         16G     0   16G   0% /dev
tmpfs           3.2G  276K  3.2G   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           6.5G     0  6.5G   0% /dev/shm
/dev/md3        1.8T   68M  1.7T   1% /home


df -i
Filesystem        Inodes  IUsed     IFree IUse% Mounted on
rootfs           1281120 247398   1033722   20% /
/dev/root        1281120 247398   1033722   20% /
devtmpfs         4105726   1516   4104210    1% /dev
tmpfs            4114099    910   4113189    1% /run
tmpfs            4114099      2   4114097    1% /run/lock
tmpfs            4114099      2   4114097    1% /dev/shm
/dev/md3       120782848     11 120782837    1% /home

Any ideas? How after ~3 GB disk can be full if I have free 1.7T?