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CSpecial Talk: Barrier-enabled IO stack for Flash Storage
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Youjip Won (School of Electrical Engineering, KAIST)
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Thursday, 31.10.2019, 11:30
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Room 601 Taub Bld.
Host:  Gala Yadgar
This work is dedicated to eliminating the overhead required for guaranteeing the storage order in the modern IO stack. The existing block device adopts a prohibitively expensive approach in ensuring the storage order among write requests: interleaving the write requests with Transfer-and-Flush. Exploiting the cache barrier command for Flash storage, we overhaul the IO scheduler, the dispatch module, and the filesystem so that these layers are orchestrated to preserve the ordering condition imposed by the application with which the associated data blocks are made durable. The key ingredients of Barrier-Enabled IO stack are Epoch-based IO scheduling, Order-Preserving Dispatch, and Dual-Mode Journaling. Barrier-enabled IO stack can control the storage order without Transfer-and-Flush overhead. We implement the barrier-enabled IO stack in server as well as in mobile platforms. SQLite performance increases by 270% and 75%, in server and in smartphone, respectively. In a server storage, BarrierFS brings as much as by 43× and by 73× performance gain in MySQL and SQLite, respectively, against EXT4 via relaxing the durability of a transaction.

Prof. Won is ICT Endowed Chair Professor at School of Electrical Engineering, KAIST. He did his BS and MS in Dept. of Computer Science, Seoul National University, Seoul, Korea in 1990 and 1992, respectively. He received his Ph. D in Computer Science from University of Minnesota in 1997. He worked for Intel Corp. as Server Performance Analyst till 1999. From 1999 till 2019, he was with Dept. of Computer Science, Hanyang University, Seoul, Korea. He was a dept. head and a director of Center for File and Storage Systems Technology (CFSR) at Hanyang University. He was awarded “Outstanding Researcher Award”, Hanyang University(2016) and “Gaheon Outstanding Research Award” from Korean Institute of Information Scientists and Engineers (KIISE)(2017). Funded by Samsung Electronics, he developed Namsan Filesystem. With Namsan Filesystem, he was awarded “Best Academy-Industry Collaboration Practice in Samsung Electronics” in 2006. Namsan Filesystem was deployed in the commercial TV products. His work on IO stack optimization in Android platform identified the root cause of the IO inefficiencies in the Android smartphones (USENIX ATC 2013, best paper award). His work on IO stack design on the Flash Storage proposes a new way of designing the filesystem, block layer and device firmware for the Flash storage (USENIX FAST 2018, best paper award). He is known for his work on the Android IO stack optimization, filesystem and block layer design for SSD and NVRAM. His research interests include Operating System, Distributed System, Storage System and Software support for byte-addressable NVRAM.
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