This version of btier seems to be very stable indeed. One of the problems that has now been solved was that btier could deadlock on high vfs cache pressure. Mostly when btier was not used with writethrough enabled on a system with limited memory.
On older releases tuning vfs_cache_pressure to 150 or higher will greatly reduce the risk of running into this problem.
echo 150 > /proc/sys/vm/vfs_cache_pressure
However upgrading to the latest version is of course the best option!
The latest release also comes with great performance.
When btier is given a PCI-e SSD as first tier, it will reach speeds of 130k random 4k iops when writethrough is disabled. It will provide around 80k of random 4k iops with writethrough enabled.
btier provides an API that provides users full control over the placement of individual data blocks.
Example code in the distribution illustrates how users can create their own data migration scripts or tools to query data placement.