Devices only filling up half way?

[Paul Migliorelli]

Hi all.  I'm trying to move and or copy a stack of files from a dir onto
an sd card 1 gig in a card reader.  Mounted as root to slash dev slash
sda1 or sdd1.  Actually this scenario is the same for the sd card in the
reader, and a 1 gig usb drive on 2 different fc6  boxes.  so I say from
root mount slash dev slash sda1 space card, where card is off my home dir.
Files get there, but after about 450 meg, it thinks no space left.  df
does show that it thinks it is a gig.  Any clues about what it may want
for any of these devices?  I know the card is cleared enough at the start
and does have the room.  Thanks.