Solid State Drive Technology - MIT Lincoln Labs
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Slideshow I presented at MIT Lincoln Labs on Thursday, March 20, 2014.
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Solid State Drive Technology - MIT Lincoln Labs
- 2. Me: • Matt Simmons • Network &Virtualization @ NEU-CCIS • Blog: Standalone SysAdmin • Email: msimmons@ccs.neu.edu • Twitter: @standaloneSA • This Slideshow: slideshare.net/standaloneSA
- 5. Variables Affecting Spinning Disk IO Rate Platter Rotational Speed Seek Speed Data Density Controller Cache
- 6. Logical Block Addressing • First introduced as an abstraction layer • Replaced CHS addressing • Address Space is Linear (block 0 - n) • Size of address space depends on the standard at time of manufacture. Disk Geometry
- 8. NOR Flash • Reads and writes are atomic single-bit • Expensive • Small specific use cases NAND Flash • Reads are based on pages or “read blocks” (4k) • Writes are based on “erasure blocks” • Cheap (and getting cheaper) • Broad use cases
- 9. The Magic Insulating Barrier Pure Silicon Doped silicon capable of holding an electrical charge
- 11. Doped Silicon Single Layer Cell (SLC) Multi-Layer Cell (MLC) Triple-Layer Cell (TLC)
- 12. Gradual Destruction Energy increases with cell layers Multiple cells need multiple writes Barrier accumulates electrons Electrical potential difference of barrier and cells disappears
- 13. Difficulty Going Forward TLC 000 100 001 101 010 110 011 111 SLC 0 1 MLC 00 01 10 11 4LC 0000 0100 1000 1100 0001 0101 1001 1101 0010 0110 1010 1110 0011 0111 1011 1111
- 14. Read / Write Profiles • Logical addresses abstracted from LBA • That abstraction can cause complexity • No seek time • Reads are generally very fast • Writes are comparatively slow
- 15. Density • 3-Dimensional • Charge levels • Size of cells • “Dot Pitch” (Cells Per Inch) • 5nm, 3nm, 2nm • Varies with “level” count
- 16. SLC / ESLC • Low Density, Quick (25µs Read / 200-300µ Write) • Write endurance near 100,000 cycles MLC / EMLC • Reasonably High Density, Slower (50µs Read / 600-900µs Write) • Write endurance near 3,000 cycles TLC • Very High Density, Even Slower (75µs Read / 900-1350µs Write) • Write endurance ~ 1,000 cycles
- 17. Write Amplification and Garbage Collection
- 18. Block Sizes • Read Block • 4k (aka “page”) • Erasure Block • (Large) multiple of 4k • aka “block” 256KB erasure block size
- 20. Write Amplification Written Data Empty Cell New Data Old Data
- 21. Write Amplification Written Data Empty Cell Old Data New Data
- 22. Write Amplification Written Data Empty Cell New data written over old cell
- 28. SSD Performance Overview • Depends on • Number of flash chips in use • Number of busses from the processor • Performance of controller CPU • Contention • Bus speed • Number of erasure blocks used • Number of previous writes to flash cells
- 29. • Chips • IO Busses • CPU Cores
- 30. Causes of Contention • Legitimate use • Garbage collection • Legitimate (but latent) useage • IO Blender! (Bender Blender: http://bit.ly/10vc7Sf)
- 31. Solid State in Practice
- 32. Solid State Form Factors Removable Media Drives PCI
- 33. Parts of an SSD
- 34. Controller Main Processor I/O Bus Lanes RAM Cache Battery / SuperCapacitor Interface
- 35. Flash Chips
- 36. Flash Controllers • Flash Translation Layer (FTL) • Stripe Writes • Interpret bus instructions • Wear Leveling • Garbage Collection
- 37. Flash Translation Layer LBA (0...n blocks) F L A S H C H I P S
- 38. SSD Aspects & Concerns
- 39. Longevity • Primarily determined by the class of flash • (e)SLC, (e)MLC,TLC • Related to wear-leveling • Under-reported capacity • Short-stroking improves lifetime (not speed)
- 40. Partition Alignment • Performance and longevity • As big (or bigger) issue than it was in spinning disks • Native 4k read blocks • Far larger erasure blocks • larger than is practical for block-size matching
- 41. TRIM/Discard • As a command,TRIM refers to ATA-8 spec • SCSI equivalent is UNMAP, but both are often referred to as TRIM. • Does not immediately delete unused blocks • Allows for GC
- 42. Linux TRIM Support • EXT4 / XFS / JFS / BTRFS - Native using ‘discard’ option • Consider NOOP or Deadline IO scheduler • Userland: • fstrim (part of util-linux) for R/W vols • zerofree for R/O vols
- 43. OSX Trim Support • Comes by default on factory-installed SSDs • Trim-Enabler • http://www.groths.org/trim-enabler/
- 44. ZFS and SSDs • ZFS Intent Log (ZIL) • Adaptive Replacement Cache (ARC) • arc_summary can help you decide
- 45. Windows • Native TRIM • Win 7, Server 2012+ • ATA TRIM • Server 2012 R2 • Manufacturer Utilities Only • < Win 7, Server 2012
- 46. Monitor Health w/ S.M.A.R.T. • S.M.A.R.T. information • vendor-specific • Includes flash erase count • smartctl on Linux and Mac • Dozens of tools on Windows (check wiki)
- 47. Forensics (http://bit.ly/fast11-wei-paper) ...Our results lead to three conclusions: ! First, built-in commands are effective, but manufacturers sometimes implement them incorrectly. ! Second, overwriting the entire visible address space of an SSD twice is usually, but not always, sufficient to sanitize the drive. ! Third, none of the existing hard drive-oriented techniques for individual file sanitization are effective on SSDs Reliably Erasing Data From Flash-Based Solid State Drives Michael Wei∗, Laura M. Grupp∗, Frederick E. Spada†, Steven Swanson∗ ∗Department of Computer Science and Engineering, University of California, San Diego †Center for Magnetic Recording and Research, University of California, San Diego
- 48. Questions?