sdcard with pc in ext4 format
putty or telnet
blkid
root@dm900:~# blkid
read here your UUID
example this and mine
/dev/mmcblk1p1: LABEL="sdcard" UUID="o43b5z32-aaz5-b101-501a-036f25fg2" TYPE="ext4" PARTUUID="3261deb1-02"
then go on fstab edit inserting your sdcard
etc/fstab
/dev/disk/by-uuid/your uuid for card /media/sdcard auto auto,nofail 0 0 insert
box reboot
df -h
your have sdcard
or install Barry Alen or userscript but you have to hang the sdcard