[dm-devel] How to use dm-cache-target?

[majianpeng]

Hi all,
    I am trying to use dm-cache-target on raid5.But i met a question.

 Supposed: /dev/sdb1(5GB) is metadata; /dev/sdb2(20GB) is cache;/dev/md0 is raid5.

1:sutup my_cache
dmsetup create my_cache --table '0 41943040 cache /dev/sdb1 /dev/sdb2 /dev/md0 131072 1 writethrough default 0'

2:mkfs.ext4
mkfs.ext4 /dev/mapper/my_cache

3:mount
mount /dev/mapper/my_cache /media

4:the size of ext4 is 20GB,but the /dev/md0 is 4TB.

I think maybe my methods error. If so, how to do use?

BTW, for dm-cache is it support plug-and-play?

Thanks!
Jianpeng Ma