Large files fail to copy to smb share!

While accessing the smb share hosted on my raspberry pi (a mounted usb hard drive)
from a ubuntu laptop via wifi I encounter two problem

1) get a disk full error when trying to copy files over to the share from the laptop,
2) if I hit "copy anyway" and the file is over 100mb aprox, it fails after a few mb.

the smb share is mounted on the laptop using fstab

here is my fstab

Code:

---

/dev/sda3      /              ext4    errors=remount-ro 0      1
//192.168.1.18/public /media/pi cifs uid=myuser,credentials=/home/myuser/.smbcredentials,iocharset=utf8,file_mode=0777,dir$
# swap was on /dev/sda5 during installation
UUID=60df05e9-f81c-493c-a338-f6fa33b2d9f5 none            swap    sw              0      0

---

my /etc/samba/smb.conf

Code:

---

[public]
  comment = Public Storage
  path = /home/shares/public
  admin users = root
  available = yes
  read only = no
  browsable = yes
  public = yes
  writeable = yes

---

any ideas where I'm going wrong?