While running in user space ZFS utilizes a user space binary called ztest. In cStor, we followed a similar approach to create a binary called ‘zrepl’ that is part of cStor. It has been built using the libraries similar to what is used for ztest and contains transactional, pooled storage layers. cStor uses ZFS behind the scenes by running it in the user space. This talk we will discuss in detail how we used ZFS in userspace for storage engine cStor and highlight a few challenges that our team faced while building this data engine.