Thank you very much for your testings and feedbacks!
In regard to persistent level-2 cache, I'm sorry that I forgot to mention the following limits. It seems that you have already known them

1. Level-2 Storage: only basic disk is supported in this version. The partition to be formatted to a level-2 storage can be a raw partition. This means that it is not necessary to format a partition with NTFS, FAT32, or other file system before formatting it to a level-2 storage.
2. In this version, level-2 cache only stores data that were discarded by level-1 cache. This means that if level-1 cache is enough large to hold all hot data, no data will be transferred to level-2 cache. Later we'll update the algorithm to make level-2 cache able to store hot data from level-1 cache.