PDF Middleware and Flash Translation Layer Co-Design for the ...

Middleware and Flash Translation Layer Co-Design for the Performance

Boost of Solid-State Drives

Chao Sun1, Asuka Arakawa1, Ayumi Soga1, Chihiro Matsui1 and Ken Takeuchi1

1Chuo University

Flash Memory Summit 2015

Santa Clara, CA

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Outline

Introduction Three Techniques to Boost SSD Performance

Storage Engine Assisted SSD SEA-SSD) Logical Block Address (LBA) Scrambler Storage Class Memory (SCM)/NAND Flash Hybrid SSD

Conclusion

Flash Memory Summit 2015

Santa Clara, CA

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Solid-State Drive

SSD is composed of NAND flash memories. SSD controller manages the data storage.

SSD

Channel-1

Way-1

Way-2

Way-m

NAND flash

NAND

...

flash

NAND flash

Host interface logic

Channel-2

SSD controller Way-1

Way-2

Way-m

NAND flash

NAND

...

flash

NAND flash

...

Channel-n

DRAM

Way-1

Way-2

NAND flash

NAND flash

Way-m

...

NAND flash

Flash Memory Summit 2015

Santa Clara, CA

[1] C. Sun et al., TCAS-I, vol. 62, no. 1, pp. 120-129, Jan. 2015.

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NAND Flash Memory

The read/write unit of the NAND flash memory is a page. The erase unit of the NAND flash memory is a block. In-place overwrite is prohibited: overwrite involves a page read + a

page write.

Bit-Line (BL)

Source-Line (SL)

Page

Block

Word-Line (WL)

Frequent overwrite create massive number of invalid pages.

Flash Memory Summit 2015

Santa Clara, CA

[1] K. Takeuchi, JSSC, vol. 44, no. 4, pp. 1227-1234, 2009.

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Garbage Collection of SSD

GC is triggered when SSD runs out of free spaces. GC can be the bottleneck of SSD write throughput.

NAND Chip

Valid page Invalid page

4. Erase the next erase block

...

Nvalid: # of valid pages

in the next erase block

Blank page

1. Read valid pages in the next erase block

Next erase block New block

...

GC latency: Nvalid x ( Tread + Twrite) + Terase

= Nvalid x 1.7ms + 8.5ms

Page copy time Erase time

If Nvalid exceeds 54, GC latency > 100ms

Page Buffer

3. Write to a new block

2. Data out/in, ECC

Flash Memory Summit 2015

SSD Controller

Santa Clara, CA

[1] K. Takeuchi, JSSC, vol. 42, no. 1, pp. 219-232, 2007.

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