Working with cache on an SSD

Hi Everybody,

Just created a backup mirror with the following command:
zpool create backup mirror /dev/sdb /dev/sdc cache /dev/sdd -m /media/BACKUP

I then did:
zfs set dedup=on backup
zfs set compression=on backup

The drive indicated by sdd is a 110 GBytes of SSD drive.
Is there a way to determine if this caching is doing its job for dedup and compression? Assuming yes - how?

Kind regards - Will