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Love/Hate Relationship between Flash Memory and Microdrive for Low-Power Portable Storage

2004. 09. 26Sang Lyul Min

Seoul National University&

Samsung Electronics

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Agenda

Overview of Portable Storage TechnologiesTechniques for High PerformanceTechniques for Low PowerConclusions

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Portable Storage Applications

Source: http://www.samsung.com/AboutSAMSUNG/InvestorRelations/ IREvents/downloads/2003_samsungforum.pdf

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The Contenders for Portable Storage Market

Portable Storage

Flash Drive

Hitachi

Samsung

LexarMediaSanDisk

Toshiba

Micro Drive

IBM Hitachi

Seagate

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Cost Comparison

$299.88 (2004.8)

$259.88 (2004.8)

$399.95 (2004.8)

Source: http://www.hitachigst.com/hdd/technolo/overview/chart03.html

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NAND Flash Memory Basics

SpareData

…

SpareData

SpareData

SpareData

SpareData

…

SpareData

SpareData

SpareData

SpareData

…

SpareData

SpareData

SpareData

………

2j blocks

2i

pages

Read physical page (chip #, block #, page #)~ 25 us

Write physical page(chip #, block #, page #)~ 300 us

Erase block(chip#, block #)~ 2 ms

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FTL (Flash Translation Layer)Definition

Software layer that makes flash memory appear to the system likea disk drive

Challenges in FTLAsymmetry in read and write speedsNo overwrite is allowed without erasing

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Logical interface for a disk drive

Operations1. Identify drive(): returns N2. Read sectors(start sector #, # of sectors)3. Write sectors(start sector #, # of sectors)

512B 512B 512B…0 1 N -1

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Block level mapping

Logical blocks

…0 1 N -1

0

…

N / 256

……

256 sectors

Sectors

Logical blocks

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Block level mapping

Logical to physical block mapping

0

… …… …

… … …

1 L

Physical blocks

Logical blocks

… …

Visible (data blocks) Invisible

…

Block mapping table

(map block)

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Read procedure

Ex. read 3 sectors from 255

0

… …… …

Block mapping table

(map block)

… … …

1 L

Physical blocks

… …

…

Logical blocks

R R R

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Write procedure (Data block update)

Ex. write 3 sectors from 255

0

… …… …

Block mapping table

(map block)

… … …

1 L

… …

…

Write buffer blocks

… … …… …

1. Erase write buffer blocks for data

W W W

2. Write data pages3. Fill remaining data pagesStill, update of mapping information is needed

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Write procedure (Map block update)

Ex. write 3 sectors from 255

0

… …… …

Block mapping table

(map block)

… … …

1 L

… …

…

Write buffer blocks

……… …WWW

4. Erase write buffer blocks for map

W

5. Read-modify-write map page6. Fill remaining map pagesStill, somewhere we need to keep the addresses of new map and write buffer blocks (i.e., logging)

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Inside Hard Disk Drive

HostInterface

CPUcore SRAM/DRAM

System Bus

Platters

USB, PCMCIA, SATA

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ATA SCSI SERIAL

SAS3Gbps

Ultra320 SCSI

Ultra160 SCSI

Ultra2 SCSIUltra SCSISCSI-3SCSI-2SCSI-1

IEEE 1394a

ATA1 ATA2 U-ATA33U-ATA66USB 2.0

USB 1.1

S-ATA1

S-ATA2

IEEE 1394b

SAS6Gbps

S-ATA3

IEEE 1394b

IEEE 1394b

Transfer Rate (MB/s)

Host Interface Performance

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HDD Form Factor and Capacity

Source: http://www.hitachigst.com/hdd/technolo/overview/chart01.html

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HDD Internal Data Rate

Source: http://www.hitachigst.com/hdd/technolo/overview/chart16.html

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Inside Flash Drive

HostInterface

FlashInterface

CPUcore SRAM

USB, PCMCIA, SATA

System Bus

Flash Chips

Flash Bus

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Flash Chip Bandwidth

Write bandwidth = 2KB/300us = 6.7MB/s per chipRead bandwidth = 2KB/25us = 80MB/s per chipErase bandwidth = 128KB/2ms = 64MB/s per chip

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Flash

Flash bus bandwidth picture

Source: Terry Lee, Micron Technology, Inc, VTF (VIA Technology Forum) 2003

20~33Mb/s per Pin

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Agenda

Overview of Portable Storage TechnologiesTechniques for High PerformanceTechniques for Low PowerConclusions

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Techniques for High Performance Flash Drive

HostInterface

FlashInterface

CPUcore SRAM

USB, PCMCIA, etc

System Bus

Flash Chips

Flash BusHigh speed Flash bus

“Sleeping with the enemy”

Multiple logical chips in a single

packaging(multi-banking)

“Getting out of the way”

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Techniques for High Performance HDD

Source: http://www.hitachigst.com/hdd/technolo/overview/chart19.html

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Agenda

Overview of Mobile Storage TechnologiesTechniques for High PerformanceTechniques for Low PowerConclusions

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Literature on Power Modeling of Portable Storage

IBM Corporation. Adaptive Power Management for Mobile Hard Drives. Technical Report, Storage Systems Division, IBM Corporation, April 1999. Available at: http://www.almaden.ibm.com/almaden/pbwhitepaper.pdf. John Zedlewski, Sumeet Sobti, Nitin Garg, Fengzhou Zheng, ArvindKrishnamurthy, and Randolph Wang. Modeling Hard-Disk Power Consumption. Proc. Second Conference on File and Storage Technologies. March 2003.Fengzhou Zheng, Nitin Garg, Sumeet Sobti, Chi Zhang, Russell E. Joseph, Arvind Krishnamurthy, and Randolph Y. Wang. Considering the Energy Consumption of Mobile Storage Alternatives. IEEE Symposium on Modeling, Analysis and Simulation of Computer Systems. October 2003.

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The Love Part: HDD+Flash Combo

+ =HDD withreduced

power consumption and start-up time

HDD NAND Flash

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Why HDD+Flash Combo?

1. Power consumption aspects:In a laptop PC, HDD consumes

~10% (~2W) total power when disk platters are spinning~1% (~0.2W) total power when disk platters are idle

2. Cost aspects:128MB Flash write buffer

< $8 in 2006< $4 in 2008

3. Reliability aspects:4. Performance aspects:

Source: Clark Nicholson, “Improved Disk Drive Power Consumption Using Solid State Non-Volatile Memory”, WinHEC2004.

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HDD+Flash Combo Block Diagram

HostInterface

FlashInterface

CPUcore SRAM

SATAFlash Chip

Flash Bus

System Bus

Platters

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Key Benefits of HDD+Flash Combo

87% reduction in power can be achieved (1.75W)Assumptions

Pavg active = ~2W (measured)Pavg with Flash write buffer and “Longhorn” kernel = 0.25W (calculated)

Toff = 600s @ .18WTon = 18s @ 2.5W

Ton = spin up time (5s) + Flash buffer flush time (13s)Flash buffer size = 128MBTransfer rate = 10MB/s

Source: Clark Nicholson, “Improved Disk Drive Power Consumption Using Solid State Non-Volatile Memory”, WinHEC2004.

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Key Considerations

1. Correctness: should preserve the semantics of HDD2. Fault tolerance and graceful degradation: should operate

correctly despite partial/total failure in flash memory3. Power efficiency: should reduce the power consumption

as much as possible4. Reliability: should improve the reliability as much as

possible5. Performance: should improve the user-perceived

performance as much as possible

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Agenda

Overview of Poratble Storage TechnologiesTechniques for High PerformanceTechniques for Low PowerConclusions

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Conclusions

In the animal worldSurvival of the fittest

In the memory worldSurvival of the fastest or cheapest

NAND FlashHDD

DRAMCheapestFRAM?SRAMFastest

Non-volatileVolatile ?

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Conclusions

From the history

Register Renaming, Out-of-order Execution,

etcCache MemoryAdditional Features

8 way4 wayMemory Interleaving

750 ns1040 nsMemory Speed

60 ns80 nsClock Rate

IBM 360/91IBM 360/85

But, IBM 360/85 faster on 8 of 11 programs!Source: David Patterson, et al., “A Case for Intelligent DRAM: IRAM”, Hot Chips VIII, August, 1996

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The Ultimate Limit – Micro Drive

FlyBy

NightBoeing 747

2,000,000 Miles Per Hour

1/100” Flying Height

Source: Richard Lary, The New Storage Landscape: Forces shaping the storage economy, 2003.

Source: http://www.hitachigst.com/

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The Ultimate Limit – Flash Drive

B/L Direction

W/L Direction

Source: K. Kim et al. IEDM Tech. Dig., 2002, pp. 919-922

200nm

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Announcement

IWSSPS 2005: International Workshop on Software Support for Portable StorageDate: March 6, 2005Place: San Francisco, USA (along with IEEE RTAS 2005 and Embedded System Conference 2005)Important Dates:

Paper Submission: December 15th 2004Notification of Acceptance: January 15th 2005Camera-ready due: February 15th 2005

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Topics of interest include, but are not limited to:- File system for portable storage- Interaction between file system and portable storage- FTL (Flash Translation Layer) for Flash memory- Power management for HDD including microdrives- DRM (Digital Right Management) for portable storage- Distributed mobile storage- Software reliability for portable storage- Software fault tolerance techniques for portable storage