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?

5.
• NAND Memory
• Controller
• Interface

6.
NAND Memory

7.
NAND Memory

8.
NAND Memory
Plane Plane
Die

9.
Plane Plane
Die

10.
Plane
Block

11.
Plane
Block
...
Block
Page Register
Cache Register

12.
Plane
Block
Page Page Page Page
...
Page Page Page Page
...
Block
Page Page Page Page
...
Page Page Page Page
Page Register
Cache Register

13.
whoa ?!

14.
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

15.
hold on to your helmets!

16.
Tunnel Oxide
Floating Gate
Fresh Cell
N- N+

17.
Programmed
Tunnel Oxide
Floating Gate
Programming puts
electrons on Floating Gate
N- N+
Floating Gate can
Permanently Store the Charge

18.
Erase
Tunnel Oxide
Floating Gate
Erase takes electrons off
the Floating Gate
N- N+

19.
Terminology Update

20.
Terminology Update
• Cell = basic memory unit
• Level = logical method to define the value of a bit

21.
cell threshold

22.
cell threshold

23.
cell threshold

24.
SLC

25.
SLC MLC
Equivalent Scale

26.
more == better ?

27.
Endurance
Performance *
FTL Capability
72nm 50nm 34nm 25nm Xnm

28.
Flash Translation Layer - FTL
• The secret sauce - i.e:
• RAID / RAISE (Redundant Array of
Independent Silicon Elements)
• GC algorithms

29.
controller

30.
controller

31.
controller
Flash Translation Layer

32.
controller
Flash Translation Layer
Block Manager

33.
controller
Flash Translation Layer
Block Manager Garbage Collector

34.
controller
Flash Translation Layer
Block Manager Garbage Collector Wear Leveler

35.
controller
Flash Translation Layer
Block Manager Garbage Collector Wear Leveler
ECC Buffer / Cache

36.
controller
Flash Translation Layer
Block Manager Garbage Collector Wear Leveler
ECC Buffer / Cache

37.
controller
Flash Translation Layer
Garbage Collector Wear Leveler
ECC Buffer / Cache

38.
controller
Flash Translation Layer
Garbage Collector Wear Leveler
ECC Buffer / Cache

39.
Erased Valid Invalid

40.
write *
Erased Valid Invalid

41.
write *
Erased Valid Invalid

42.
write *
Erased Valid Invalid

43.
write *
Erased Valid Invalid

44.
write *
(re) - Read
Erased Valid Invalid

45.
write / erase / TRIM
write *
(re) - Read
Erased Valid Invalid

46.
write / erase / TRIM
write *
(re) - Read
Erased Valid Invalid

47.
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

48.
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

49.
Erased New Used

50.
Erased New Used
Invalid
Written-to / Erased

51.
New Data
• Whole blocks must be erased &
written
• Writes Speed is affected

52.
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

53.
Endurance
• User Created
• Internal Activity
• GC, Wear Leveling, Page Remapping
• Overprovisioning
• Write Amplification

54.
ssd latency over time
• source : tintri

55.
interface
• Yesterday : SATA / SAS
• Today : PCIe
• Tomorrow : SCSI Express

56.
thank you
now ask me something … please