Optimizing Performance and Reliability of Mobile Storage Memory

Transcription

1 Optimizing Performance and Reliability of Mobile Storage Memory 8/5/14 You Sung Kim SK hynix America, Inc. August

2 Memory Trend PC Era (1980~) CPU centric (GHz spec.) Smart & Mobile Era (2007~) Mobile experience centric (always connected) Next Waves (2014~) customized usages (high performance, reliable) Number of Devices Time August

3 Mobile Storage Requirements Applications demand mobile storages of high performance and reliability Application Client Network Server Usages Main storage Boot, cache Boot, storage Power Ultra Low Low Low Form Factor Ultra Small Small Small Performance High Mid to High Mid to High Reliability Mid to High High High August

4 Challenges of NAND Flash Performance Host access is basically random Sequential is more natural in NAND Reliability Life span restriction due to endurance Data could be lost after exceeding retention spec. How to get the most from Flash storage device? August

5 NAND configuration Sequential access is more natural than random Random access requires NAND page changes with performance overhead and more wear out NAND structure Block BL(N+1) BL(N) NAND Page<N> (Block<X> : WL<I>) Page <M> (Block<Y> : WL<J>) * Random Access (Slow) CHANNEL Data Buffer * Sequential Read Busy Ready NAND Controller Access (Fast) Write Busy Ready Cache Buffer * Busy : overhead per page change August 2014 Host 5

6 Performance Asymmetry Sequential vs. random asymmetry continues Cache buffer size restriction due to cost, power, etc. MB/s * booting, installing, recording, playback Max. Interface IOPS * Concurrent use cases (swapping, switching, multi-threaded apps) random read sequential read 5000 random write 0 emmc 4.41 emmc 4.5 emmc 5.0 sequential write UFS 2.0 Gear2 UFS 2.0 Gear3 0 emmc 4.41 emmc 4.5 emmc 5.0 UFS 2.0 Gear2 UFS 2.0 Gear3 August

7 Life Span by endurance Life span depends on Max. host usage and how many writes NAND allows. Larger chunk size and address alignment can help life span longer. Life Span [yrs] WAI vs. chunk size * NAND Density * NAND Cycles = WAI * Yearly Usage (Max) WAI (Wear Acceleration Index) Actual Size written to NAND = Data size written by host WAI [normalized] chunk size [KB] * Random access August

8 Life Span [yrs] Life span calculator Input : Max. GB per year, P/E cycle, Density Chunk size optimization and address alignment can help before (misaligned) before (aligned) after (misaligned) after (aligned) Applications Max GB/year % of total GB/yr Before chunk optimization (misaligned) Chunk size [KB) After chunk optimization (Aligned) application % 1 1 application % 4 32 application % 4 32 application % 4 32 application % 4 64 application % 4 32 application % application % 4 32 application % 4 4 application % 4 4 application % 4 32 application % 1 1 application % 1 1 application % 4 4 application % 4 32 application % 4 4 total NAND Density [GB] NAND cycles per block Life Span [yrs] August

9 Refresh period calculator Refresh period depends on Min. host usage and wear leveling policy of NAND storage. WAI and wear leveling optimization is necessary Refresh period [yrs] Refresh period vs. WLT = NAND Density * WLT WAI * Yearly Usage (Min) WLT (Wear Leveling Threshold) WLT Erase Count Refresh period (Years) WLT128_1.26G NAND Block Address (physical) * User density = 64GB * Min. Usage = 1.26GB/day August WAI WLT64_1.26G WLT32_1.26G Retention Spec. =< (MLC)

10 Refresh algorithms Customized solutions to refresh NAND blocks before retention spec. 1) Self Refresh 2) Refresh by host (vendor command) Read page<i> Set # of block per refresh cmd [M] Block<0> Block<1> N # of Error bit > threshold Copy page<i> to page<j> Update mapping table End Y Repeat until N+M Read pointer to start refresh [N] Copy Block<N> to Spare Block <N> put Block<N> to Spare Block pool Set refresh pointer as N+M User Area Spare Queue Block<End> Spare Block<0> Spare Block<1> Spare Block<End> August

11 Summary Performance Larger chunk and alignment can help storage performance better Reliability Refer to both Life span and refresh period calculators Chunk optimization and alignment can help storage working longer Refresh algorithms as backup solutions Better understanding gives better result!! August

12 For more discussions Welcome to visit SK hynix Booth #310 ^^ August