Solid-State Drives (SSDs)csl.skku.edu/uploads/ICE3028S11/4-ssd.pdf · Feature SSD (Samsung) HDD (Seagate) Model MMDOE56G5MXP (PM800) ST9500420AS (Momentus 7200.4) Capacity 256GB (16Gb

Jin-Soo Kim (jinsookim@skku.edu)Computer Systems Laboratory

Sungkyunkwan Universityhttp://csl.skku.edu

Solid-StateDrives (SSDs)

Solid-State Drives (SSDs)

ICE3028: Embedded Systems Design (Spring 2011) – Jin-Soo Kim (jinsookim@skku.edu) 3

HDDs vs. SSDs (1)

2.5” HDD Flash SSD(101x70x9.3mm)

1.8” HDD Flash SSD(78.5x54x4.15mm)

Top Bottom

HDDs vs. SSDs (2)

1 Source: http://forums.macrumors.com/showthread.php?t=658571 2 Source: http://www.danawa.com (As of Mar. 17, 2011)

Feature SSD (Samsung) HDD (Seagate)

Model MMDOE56G5MXP (PM800) ST9500420AS (Momentus 7200.4)

Capacity 256GB(16Gb MLC x 128, 8 channels)

500GB(2 Discs, 4 Heads, 7200RPM)

Form factor 2.5”Weight: 84g

2.5”Weight: 110g

Host interface Serial ATA-2 (3.0 Gbps)Host transfer rate: 300MB

Serial ATA-2 (3.0 Gbps)Host transfer rate: 300MB

Power consumption Active: 0.26WIdle/Standby/Sleep: 0.15W

Active: 2.1W (Read), 2.2W (Write)Idle: 0.69W, Standby/Sleep: 0.2W

Performance Sequential read: Up to 220 MB/sSequential write: Up to 185 MB/s

Power-on to ready: 4.5 secAverage latency: 4.17 msec

Measured performance1

(On MacBook Pro,256KB for sequential, 4KB for random)

Sequential read: 176.73 MB/sSequential write: 159.98 MB/sRandom read: 10.56 MB/sRandom write: 2.93 MB/s

Sequential read: 86.07 MB/sSequential write: 84.64 MB/sRandom read: 0.61 MB/sRandom write: 1.28 MB/s

Price2 539,190 won 80,400 won

NAND Constraints

No In-Place Update

▪ Can’t overwrite data ▪ Previous data should be erased▪ The erase unit is much larger than the

read/write unit• Read/write unit: page (4KB, 8KB)• Erase unit: block (64 ~ 128 pages)

Bit Errors▪ Error correction codes (ECC) in spare area▪ Hardware vs. software

Source: Micron Technology, Inc.

Bad Blocks

▪ Factory-marked bad blocks▪ Run-time bad blocks

▪ Bad block table▪ Bad block remapping

Limited Lifetime

▪ Limited program/erase cycles▪ 100K for SLCs▪ 5K ~ 10K for MLCs▪ Wear-leveling

Page Programming▪ NOP

• The number of partial-page programming is limited

• 1 / sector for most SLCs (4 for 2KB page)• 1 / page for most MLCs

▪ Sequential page programming• Pages should be programmed sequentially

inside a block• For large block SLCs and MLCs

Paired Pages in MLCs▪ Performance difference▪ Interference

11 10 01 00 Page 0

11 10 01 00

MSB Page LSB Page

I/O-split MLCs

Page-split MLCs

Beauty and the Beast▪ NAND Flash memory is beauty

• Small, light-weight, robust, low-cost, low-power non-volatile device

▪ NAND Flash memory is a beast• Much slower program/erase operations• No in-place-update• Erase unit > write unit• Limited lifetime (5K ~ 100K P/E cycles)• Bad blocks, …

Introduction toFlash Translation Layers

Storage Abstraction▪ Abstraction given by block device drivers:

▪ Operations• Identify(): returns N• Read (start sector #, # of sectors)• Write (start sector #, # of sectors, data)

512B 512B 512B

0 1 N-1

Source: Sang Lyul Min (Seoul National Univ.)

What is FTL?▪ A software layer to make NAND flash fully

emulate traditional block devices (or disks)

+Device Driver

Read Write Erase

File System

Read Sectors Write Sectors

Flash Memory

Mismatch!

+Device Driver

Flash Memory

File System

Source: Zeen Info. Tech.

Flash Cards Internals

SSD Internals

Implementing FTLs

Applications

Operating System

File Systems

Block Device Driver

Flash Translation Layer

NAND Controller

NAND Flash Memory

Applications

Operating System

File Systems

Block Device Driver

Flash Translation Layer

NAND Controller

NAND Flash Memory

Flash Cards, SSDs Embedded Flash Storage

For Performance▪ Indirect mapping (address translation)▪ Garbage collection▪ Over-provisioning▪ Hot/cold data identification/separation▪ Interleaving over multiple channels/flash

chips/planes▪ Request scheduling▪ Buffer management, …

For Reliability

▪ Bad block management▪ Wear-leveling▪ Power-off recovery▪ Error correction code (ECC)▪ ...

Other Features

▪ Encryption▪ Compression▪ Deduplication▪ ...

Basic Mapping Techniques

Naïve Block Mapping▪ Each table entry maps one block▪ Small RAM usage▪ Inefficient handling of small writes

00112233

44556677

889910101111

1212131314141515

LBN 0LBN 0LBN 1LBN 1LBN 2LBN 2LBN 3LBN 3

Data blocks

00000010 11

Logicalblock number

Page offset within a block

Logical page #11

Example (1)▪ W = <{4,5,6,7}, {1}>

• write ({4,5,6,7}, ABCD)

00112233

889910101111

1212131314141515

Data blocks

Spareblocks

AABBCCDD

Example (2)▪ W = <{4,5,6,7}, {1}>

• write ({4,5,6,7}, ABCD)• write ({1}, E)

889910101111

1212131314141515

Data blocks

Spareblocks

AABBCCDD

00EE2233

ANAND Scheme▪ M-Systems ▪ US Patent 5,937,425▪ Uses one or more

replacement blocks▪ Data is written to

an unwritten physical page with the desired physical page offset

Data blocks

891011

Replacementblocks

W = <{1}, {4,5}, {8}, {10}, {8}>

Naïve Page Mapping▪ Most flexible▪ Efficient handling of small

writes▪ Large memory footprint

• 32MB for 32GB MLC (4KB page)

▪ Sensitive to the amount of reserved blocks

▪ Performance affected as the system ages

0011441414

1010556677

228811111313

151599331212

Data blocks

LPN 0LPN 0LPN 1LPN 1LPN 2LPN 2LPN 3LPN 3LPN 4LPN 4LPN 5LPN 5LPN 6LPN 6LPN 7LPN 7LPN 8LPN 8LPN 9LPN 9LPN 10LPN 10LPN 11LPN 11LPN 12LPN 12LPN 13LPN 13LPN 14LPN 14LPN 15LPN 15

Example (1)▪ W = <{1}, {2}, {8}, {1}, {2}, {12,13}, {9}>

• write ({1}, A)

001441414

1010556677

228811111313

151599331212

Data blocks

Spareblocks

Example (2)▪ W = <{1}, {2}, {8}, {1}, {2}, {12,13}, {9}>

• write ({1}, A)• write ({2}, B)

001441414

1010556677

28811111313

151599331212

Data blocks

Spareblocks

Example (3)▪ W = <{1}, {2}, {8}, {1}, {2}, {12,13}, {9}>

• write ({1}, A)• write ({2}, B)• write ({8}, C)

001441414

1010556677

2811111313

151599331212

Data blocks

AABBCC

Spareblocks

Example (4)▪ W = <{1}, {2}, {8}, {1}, {2}, {12,13}, {9}>

• write ({1}, A)• write ({2}, B)• write ({8}, C)• write ({1}, D)

001441414

1010556677

2811111313

151599331212

Data blocks

ABBCCDD

Spareblocks

Example (5)▪ W = <{1}, {2}, {8}, {1}, {2}, {12,13}, {9}>

• write ({1}, A)• write ({2}, B)• write ({8}, C)• write ({1}, D)• write ({2}, E)

001441414

1010556677

2811111313

151599331212

Data blocks

ABCCDD

Spareblocks

Example (6)▪ W = <{1}, {2}, {8}, {1}, {2}, {12,13}, {9}>

• write ({1}, A)• write ({2}, B)• write ({8}, C)• write ({1}, D)• write ({2}, E)• write ({12,13}, FG)

001441414

1010556677

28111113

1515993312

Data blocks

ABCCDD

Spareblocks

EEFFGG

Example (7)▪ W = <{1}, {2}, {8}, {1}, {2}, {12,13}, {9}>

• write ({1}, A)• write ({2}, B)• write ({8}, C)• write ({1}, D)• write ({2}, E)• write ({12,13}, FG)• write ({9}, H)

001441414

1010556677

28111113

151593312

Data blocks

ABCCDD

Spareblocks

EEFFGGHH

Victim Selection Policies▪ Greedy

• A block with the largest amount of invalid data

▪ Cost-benefit [Kawaguchi 1995]• A block with the maximum • u: utilization• age: the time sine the most recent modification

▪ Cost Age Times (CAT) [Chiang 1999]• A block with the minimum• count: erase count

costbenefit

countageu

Solid-State Drives (SSDs)csl.skku.edu/uploads/ICE3028S11/4-ssd.pdf · Feature SSD (Samsung) HDD (Seagate) Model MMDOE56G5MXP (PM800) ST9500420AS (Momentus 7200.4) Capacity 256GB (16Gb

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