A New LSM-style Garbage Collection Scheme for ZNS SSDs.

This paper explores how to design a garbage collection scheme for ZNS (Zoned NameSpace) SSDs (Solid State Drives). We first show that a naive garbage collection based on a zone unit incurs a long latency due to the huge size of a zone. To overcome this problem, we devise a new scheme, we refer to it as LSM ZGC (Log-Structured Merge style Zone Garbage Collection), that makes use of the following three features: segment based fine-grained garbage collection, reading both valid and invalid data in a group manner, and merging different data into separate zones. Our proposal can exploit the internal parallelism of a zone and reduce the utilization of a candidate zone by segregating hot and cold data. Real implementation based experimental results show that our scheme can enhance performance by 1.9 times on average.