ramcache

mkdir /mnt/tmpfs
mount -t tmpfs -o size=4G none /mnt/tmpfs
dd if=/dev/zero of=/mnt/tmpfs/disk4G.img bs=1 count=0 seek=4G
losetup loop0 /mnt/tmpfs/disk4G.img
mdadm  --create /dev/md0 --run --level=linear --raid-devices=2 /dev/loop0 /dev/sdX
mkdir /mnt/ramcache
mount /dev/md0 /mnt/ramcache