Storage Class Memory: Technology Overview & System Impacts

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This slides introduce a novel storage device SCM and its impacts!

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Storage Class Memory: Technology Overview & System Impacts

  1. 1. Phase Change MemoryStorage Class Memory:Technology Overview & System ImpactsZhichao Liangfrankey0207@gmail.comStorage Class Memory
  2. 2. Phase Change MemoryOutline• Why & what is storage class memory?• A typical storage class memory device: PCM• The impacts of SCM on database system• ConclusionStorage Class Memory
  3. 3. Phase Change MemoryOutline• Why & what is storage class memory?• A typical storage class memory device: PCM• The impacts of SCM on database system• ConclusionStorage Class Memory
  4. 4. Phase Change MemoryChallenges in building large systems• Power and coolingStorage Class Memory
  5. 5. Phase Change MemoryChallenges in building large systems (cont.)• Latency gap between CPU and diskStorage Class Memory
  6. 6. Phase Change MemoryHDD access timeStorage Class Memory
  7. 7. Phase Change MemoryHDD access time (cont. ) Access time rotation time seek time HDD with a faster than HDD size will transform 15,000 rpm almost from 3.5-inch to 2.4-inch impossible within the and then 1.8-inch for the next 10 years! best case.Storage Class Memory
  8. 8. Phase Change MemoryHDD power• The power P supplied to a disk drive is given by P = I + M +S. - I : power for interface & control logic; - M: motor to spin the disk; - S : move head to the new track. I & M already close to S can be improved on smaller their theoretical size disk drive or shutting down efficiency limits! completely when not in use!Storage Class Memory
  9. 9. Phase Change MemorySSD disadvantage• The short life time of SSD is an obstacle for its use in industrial-length applications. Device Endurance DRAM 10 power 15 Disk drive 10 power 12 Flash memory 10 power 4 ~ 5• The limited scalability of SSD hinder its capacity increasing & price decreasing.Storage Class Memory
  10. 10. Phase Change MemoryDefinition of SCM• Storage Class Memory (SCM) is IBM’s term for a new class of data storage and memory devices.• SCM blurs the distinction between Memory (fast, expensive, volatile) and Storage (slow, cheap, non-volatile).• Features of SCM: - Solid state, no moving parts - Short Access times (within an order-of-magnitude of DRAM) - Low cost per bit (DISK like, within an order-of-magnitude) - Non-volatile ( ~ 10 years)Storage Class Memory
  11. 11. Phase Change MemoryLatency gap with SCM Read/Write PCM (100 – 1000 ns) SCMStorage Class Memory
  12. 12. Phase Change MemoryEvolution of memory/storage stackStorage Class Memory
  13. 13. Phase Change MemoryCandidate SCM devices• Improved Flash - little change expected in write endurance or speed• FeRAM (Ferroelectric RAM) - FeFET• MRAM (Magnetic RAM) Phace-change - Racetrack memory RAM (PCM)• RRAM (Resistive RAM) - Organic & polymer memory• PC-RAM (Phase-change RAM)Storage Class Memory
  14. 14. Phase Change MemoryOutline• Why & what is storage class memory?• A typical storage class memory device: PCM• The impacts of SCM on database system• ConclusionStorage Class Memory
  15. 15. Phase Change MemoryPhase change memory• Phase change memory (PCM) is the leading contender for first true SCM.• At least 18 companies are working on PCM, such as Samsung, IBM, Intel, Micro, etc.• PCM is an electronic device using two distinct solid phases of a metal alloy to store a bit.Storage Class Memory
  16. 16. Phase Change MemoryPCM basic concept• Ge-Sb-Te exists in a (quasi)stable amorphous and a stable crystalline phase. - Phases have very different electrical resistances – ratio of 1:100 to 1:1000, and different optical reflectivity.• Transition between phases by controlled heating and cooling - Write ‘1’ (SET) : longer (50ns) weaker current pulse - Write ‘0’ (RESET) : short (10ns) intense current pulse - Read : short weak pulse senses resistanceStorage Class Memory
  17. 17. Phase Change MemoryPCM A data cell at each of the intersections of a wordline and a bitline! Slow crystallization affects write performance!Storage Class Memory
  18. 18. Phase Change MemoryPCM vs DRAM Device Type DRAM PCM-S PCM-M Capacity 16GB 128GB 16GB Feature Size 32nm 32nm 32nm Read Latency 60ns 800ns 300ns Write Latency 60ns 1400ns 1400ns Retention Time ms 2-10 years dependent Write Endurance 10 power 15 10 power 8 10 power 12 An SCM cell at the maximum write times would be worn out within a few minutes! So a wear-leveling layer maybe necessary!Storage Class Memory
  19. 19. Phase Change MemoryTaxonomy of PCM system uses Memory Oriented: Storage Oriented: 1) PCM replaces DRAM 1) PCM replaces HDD/SSD completely; completely; 2) PCM stands by DRAM. 2) PCM as the cache of HDD/SSD. PCM replaces DRAM completely: L2 & L3 PCM CPU PCM cache controlStorage Class Memory
  20. 20. Phase Change MemoryTaxonomy of PCM system uses Memory Oriented: Storage Oriented: 1) PCM replaces DRAM 1) PCM replaces HDD/SSD completely; completely; 2) PCM stands by DRAM. 2) PCM as the cache of HDD/SSD. PCM stands by DRAM: DRAM CPU VM contol PCM PCM controlStorage Class Memory
  21. 21. Phase Change MemoryTaxonomy of PCM system uses Memory Oriented: Storage Oriented: 1) PCM replaces DRAM 1) PCM replaces HDD/SSD completely; completely; 2) PCM stands by DRAM. 2) PCM as the cache of HDD/SSD. PCM replaces HDD/SSD completely: 1) Via legacy I/O buses? CPU I/O control PCM 2) Via new PCM control interface? 3) Page device ?Storage Class Memory
  22. 22. Phase Change MemoryTaxonomy of PCM system uses Memory Oriented: Storage Oriented: 1) PCM replaces DRAM 1) PCM replaces HDD/SSD completely; completely; 2) PCM stands by DRAM. 2) PCM as the cache of HDD/SSD. PCM as the cache of HDD/SSD: PCM DRAM I/O control PCM HDD controlStorage Class Memory
  23. 23. Phase Change MemoryOutline• Why & what is storage class memory?• A typical storage class memory device: PCM• The impacts of PCM on database system• ConclusionStorage Class Memory
  24. 24. Phase Change Memory Database system overview Read & Write Applications Access Methods Transaction Data Page & Log File LockB+ Tree Index Hash Index Buffer Pool HDD LRU, Clock LogStorage Class Memory
  25. 25. Phase Change MemoryPCM replaces DRAM• PCM buffer pool access (300ns) will be slower than DRAM buffer pool access (60ns).• PCM buffer pool write (1400ns) will be slower than DRAM buffer pool write (60ns).• Data durability can be guaranteed even database server restart or power off.• What about logging? Logging is still necessary?• Wear-leveling can be a problem!• Rethink of buffer pool replacement strategy!Storage Class Memory
  26. 26. Phase Change MemoryPCM replaces DRAM (cont.)• PCM buffer pool access (300ns) will be slower than DRAM buffer pool access (60ns).• PCM buffer pool write (1400ns) will be slower than DRAM buffer pool write (60ns). How to reduce Asymmetric read & write on PCM write on PCM• Data durability can be guaranteed even database server restart or power off.• What about logging? Logging is still necessary?• Wear-leveling can be a problem!• Rethink of buffer pool replacement strategy!Storage Class Memory
  27. 27. Phase Change MemoryPCM with DRAM• Using PCM to extend the DRAM, older data in DRAM will be transmitted to PCM.• Or using PCM and DRAM in parallel mode.• Complete data durability can not be guaranteed but can be improved much.• Rethink of buffer pool replacement strategy!• How to make use of DRAM and PCM to achieve the optimized lifetime of PCM.Storage Class Memory
  28. 28. Phase Change MemoryPCM with DRAM (cont.)• Using PCM to extend the DRAM, older data in DRAM will be transmitted to PCM.• Or using PCM and DRAM in parallel mode. Data Cool and hot• Complete data durability can not beplacement but data guaranteed can be improved much. distinction strategy• Rethink of buffer pool replacement strategy!• How to make use of DRAM and PCM to achieve the optimized lifetime of PCM.Storage Class Memory
  29. 29. Phase Change MemoryPCM replaces HDD• In the near future, the capacity of PCM won’t be as much as disk.• Even if whole DB fits in PCM and even though PCM is persistent, still need to externalize DB regularly, since PCM won’t have good endurance!• In-memory buffer pool can be obviated, or at least read buffer can be obviated.• The read performance of DBMS can be improved much, whatever sequential read or random read.Storage Class Memory
  30. 30. Phase Change MemoryPCM replaces HDD (cont.)• Hardware-enforced block boundaries, such as sector on HDD and page on SSD, are eliminated. - Unlikely large amounts of data become suddenly unavailable - More likely bits, or small ranges of bytes will fail together - Eliminates need for read-modify-write for small updates• Opportunity to rethink data structures for implementing database system, such as B+ Tree, record organization, etc.Storage Class Memory
  31. 31. Phase Change MemoryPCM with HDD• Using PCM to extend HDD, fresh data in PCM & older data in HDD.• Or using PCM for special use, e.g., storing index data on PCM or logging data on PCM.• The write performance can be improved much, whatever sequential write or random write.• How to reduce the amount of write when storing index data on PCM?• The best configuration of PCM & HDD capacity?Storage Class Memory
  32. 32. Phase Change MemoryConclusion• SCM is an promising technology for building large storage system.• PCM has some special characteristics different from HDD & SSD, which need to be reconsidered for system design.• Research on PCM-based database system just catch the attention of researchers and a lot opportunities are there.Storage Class Memory
  33. 33. Phase Change MemoryQ&AStorage Class Memory

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