New Reliable Storage System On Multiple Open-Channel SSDs

Solid state drives(SSDs)are now widely used in various storage systems.Similar to hard disks,Redundant Array of Independent Disks(RAID)can be built on multiple SSDs to provide data reliability.However,the traditional RAID is difficult to expand,and the recovery process is slow when device errors occur,and the data storage flexibility is low.Besides,parity update in RAID5 will bring high cost.Especially in random write,one data write needs four random IOs to do.Setting up RAID directly on SSDs not only has these problems but also has serious parity update issue.The latest SSD technology OpenChannel SSD exposes internal details to the upper layer software,allowing the upper layer software to control data placement and IO scheduling,which brings new ideas to the design of storage systems with data reliability on SSDs.Based on the observations above,this paper designs and implements NROCS(New Reliable Storage System on Open-Channel SSDs).NROCS combines data reliability techniques in the upper layer with underlying Open-Channel SSDs,eliminating problems of building RAID5 on conventional SSDs,which can improve performance and protect the lifespan of SSDs.Main contributions of this paper are:· As far as we know,this paper is the first to build a reliable data storage system called NROCS on multiple Open-Channel SSDs.· Instead of the fixed data layout in RAID5,NROCS decides where to store data at run-time.NROCS adopts a log-structured way to write data,so that parity update doesn't need to read any data and the parity write itself can be consolidated,which can eliminate the parity update issue existing in RAID5.The flexible data placement allows users of NROCS to customize their wear-leveling strategies.It is easier to expand the capacity of NROCS because new drive will not change address map-ping.Besides,NROCS can recover from errors in fine-grained granularity,which can reduce the cost of recovery process.· This paper implements NROCS in Linux kernel,and evaluates NROCS5 with FIO,Filebench and Rocks DB.The experimental results show that NROCS reduces 33% data writes at most and achieves 127%× ~ 905%× speedup.