1. Flash 101
roman tarnavski - @romant

2. • iPods
• Laptops
• Cameras
• Enterprise Arrays
• Embedded Devices

3. why?
• computer buses and networks are faster
• electromechanical disk drives are slower
• colder to run
• faster to execute
• slower to die*

4. What’s inside?

6. • NAND Memory
• Controller
• Interface

7. NAND Memory

8. NAND Memory

9. NAND Memory
Plane Plane
Die

10. Plane Plane
Die

14. Plane
Block

15. Plane
Block
...
Block
Page Register
Cache Register

16. Plane
Block
Page Page Page Page
...
Page Page Page Page
...
Block
Page Page Page Page
...
Page Page Page Page
Page Register
Cache Register

17. whoa ?!

18. SLC / MLC / eMLC / TLC …
Features SLC MLC
Bits per cell 1 2
Endurance (erase/write cycles) 100,000 10,000
Read service time (max) 25µs 50µs
Write service time (typical) 200–300µs 600–900µs
Block Erase (typical) 1.5 - 2 ms 2 ms

19. hold on to your helmets!

20. Tunnel Oxide
Floating Gate
Fresh Cell
N- N+

21. Programmed
Tunnel Oxide
Floating Gate
Programming puts
electrons on Floating Gate
N- N+
Floating Gate can
Permanently Store the Charge

22. Erase
Tunnel Oxide
Floating Gate
Erase takes electrons off
the Floating Gate
N- N+

23. Terminology Update

24. Terminology Update
• Cell = basic memory unit
• Level = logical method to define the value of a bit

26. cell threshold

27. cell threshold

28. cell threshold

29. SLC

30. SLC MLC
Equivalent Scale

31. more == better ?

32. Endurance
Performance *
FTL Capability
72nm 50nm 34nm 25nm Xnm

33. Flash Translation Layer - FTL
• The secret sauce - i.e:
• RAID / RAISE (Redundant Array of
Independent Silicon Elements)
• GC algorithms

34. controller

35. controller

36. controller
Flash Translation Layer

37. controller
Flash Translation Layer
Block Manager

38. controller
Flash Translation Layer
Block Manager Garbage Collector

39. controller
Flash Translation Layer
Block Manager Garbage Collector Wear Leveler

40. controller
Flash Translation Layer
Block Manager Garbage Collector Wear Leveler
ECC Buffer / Cache

41. controller
Flash Translation Layer
Block Manager Garbage Collector Wear Leveler
ECC Buffer / Cache

42. controller
Flash Translation Layer
Garbage Collector Wear Leveler
ECC Buffer / Cache

43. controller
Flash Translation Layer
Garbage Collector Wear Leveler
ECC Buffer / Cache

45. Erased Valid Invalid

46. write *
Erased Valid Invalid

47. write *
Erased Valid Invalid

48. write *
Erased Valid Invalid

49. write *
Erased Valid Invalid

50. write *
(re) - Read
Erased Valid Invalid

51. write / erase / TRIM
write *
(re) - Read
Erased Valid Invalid

52. write / erase / TRIM
write *
(re) - Read
Erased Valid Invalid

53. Blocks vs. Pages
Block
• Made up of • Basic storage unit
• 32 / 64 / 128 pages • Has no standard
capacity
• Assembled in RAM Block
and written whole • 4 / 8 / 16 KB

54. Blocks vs. Pages
Block
Page Page Page Page
• Made up of • Basic storage unit
...
• •
Page Page Page Page
32 / 64 / 128 pages Has no standard
capacity
• Assembled in RAM Block
and written whole
Page Page Page Page
• 4 / 8 / 16 KB
Page Page
...
Page Page

55. Erased New Used

56. Erased New Used
Invalid
Written-to / Erased

57. New Data
• Whole blocks must be erased &
written
• Writes Speed is affected

58. By Example - Efficiency 101
• Writing 4 K will at
• 25nm die, 8GB chip worst:
• Page Size: 8 KB • Read ~2 MB
• Block Size: 256 pages • Append 4K
= 2048 KB
• Write 2 MB

59. Endurance
• User Created
• Internal Activity
• GC, Wear Leveling, Page Remapping
• Overprovisioning
• Write Amplification

60. ssd latency over time
• source : tintri

61. interface
• Yesterday : SATA / SAS
• Today : PCIe
• Tomorrow : SCSI Express

62. thank you
now ask me something … please