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Flash 101

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Roman Tarnavski
Roman Tarnavski

An explanation of how silicon-wafer-totting droids translate to a read+write operation of an SSD device. Presented at Sydney VMUG 2012Q2. Best downloaded and played with Keynote for animations.

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Flash 101 roman tarnavski - @romant
• iPods • Laptops • Cameras • Enterprise Arrays • Embedded Devices
why? • computer buses and networks are faster • electromechanical disk drives are slower • colder to run • faster to execute • slower to die*
What’s inside?
Flash 101
• NAND Memory • Controller • Interface
NAND Memory
NAND Memory
NAND Memory Plane Plane Die
Plane Plane Die
Flash 101
Flash 101
Flash 101
Plane Block
Plane Block ... Block Page Register Cache Register
Plane Block Page Page Page Page ... Page Page Page Page ... Block Page Page Page Page ... Page Page Page Page Page Register Cache Register
whoa ?!
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
hold on to your helmets!
Tunnel Oxide Floating Gate Fresh Cell N- N+
Programmed Tunnel Oxide Floating Gate Programming puts electrons on Floating Gate N- N+ Floating Gate can Permanently Store the Charge
Erase Tunnel Oxide Floating Gate Erase takes electrons off the Floating Gate N- N+
Terminology Update
Terminology Update • Cell = basic memory unit • Level = logical method to define the value of a bit
Flash 101
cell threshold
cell threshold
cell threshold
SLC
SLC MLC Equivalent Scale
more == better ?
Endurance Performance * FTL Capability 72nm 50nm 34nm 25nm Xnm
Flash Translation Layer - FTL • The secret sauce - i.e: • RAID / RAISE (Redundant Array of Independent Silicon Elements) • GC algorithms
controller
controller
controller Flash Translation Layer
controller Flash Translation Layer Block Manager
controller Flash Translation Layer Block Manager Garbage Collector
controller Flash Translation Layer Block Manager Garbage Collector Wear Leveler
controller Flash Translation Layer Block Manager Garbage Collector Wear Leveler ECC Buffer / Cache
controller Flash Translation Layer Block Manager Garbage Collector Wear Leveler ECC Buffer / Cache
controller Flash Translation Layer Garbage Collector Wear Leveler ECC Buffer / Cache
controller Flash Translation Layer Garbage Collector Wear Leveler ECC Buffer / Cache
Flash 101
Erased Valid Invalid
write * Erased Valid Invalid
write * Erased Valid Invalid
write * Erased Valid Invalid
write * Erased Valid Invalid
write * (re) - Read Erased Valid Invalid
write / erase / TRIM write * (re) - Read Erased Valid Invalid
write / erase / TRIM write * (re) - Read Erased Valid Invalid
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
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
Erased New Used
Erased New Used Invalid Written-to / Erased
New Data • Whole blocks must be erased & written • Writes Speed is affected
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
Endurance • User Created • Internal Activity • GC, Wear Leveling, Page Remapping • Overprovisioning • Write Amplification
ssd latency over time • source : tintri
interface • Yesterday : SATA / SAS • Today : PCIe • Tomorrow : SCSI Express
thank you now ask me something … please

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Flash 101

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