Flash 101

Flash 101roman 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?

• NAND Memory• Controller• Interface

NAND Memory

NAND Memory Plane Plane Die

Plane Plane Die

PlaneBlock

Plane Block ... BlockPage RegisterCache Register

Plane BlockPage Page Page Page ...Page Page Page Page ... BlockPage Page Page Page ...Page Page Page Page Page Register Cache Register

whoa ?!

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

hold on to your helmets!

Tunnel OxideFloating Gate Fresh Cell N- N+

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

Erase Tunnel OxideFloating 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

cell threshold

SLC MLC Equivalent Scale

more == better ?

Endurance Performance * FTL Capability72nm 50nm 34nm 25nm Xnm

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

controller

controllerFlash Translation Layer

controllerFlash Translation Layer Block Manager

controllerFlash Translation Layer Block Manager Garbage Collector

controllerFlash Translation Layer Block Manager Garbage Collector Wear Leveler

controllerFlash Translation Layer Block Manager Garbage Collector Wear Leveler ECC Buffer / Cache

controllerFlash Translation Layer Garbage Collector Wear Leveler ECC Buffer / Cache

Erased Valid Invalid

write *Erased Valid Invalid

write * (re) - ReadErased Valid Invalid

write / erase / TRIM write * (re) - ReadErased 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 younow ask me something … please

Flash 101

by Roman Tarnavski on Jun 26, 2012

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Flash 101

by Roman Tarnavski on Jun 26, 2012

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Flash 101 Presentation Transcript

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