NAND Fl hNAND Flash-bd based Storagecsl.skku.edu/uploads/CSE3008F09/16-flash.pdf · 2011. 2. 14. · SSDs(2)SSDs (2) Feature SSD (Samsung) HDD (Seagate) Model MMDOE56G5MXP (PM800)

NAND Fl h b d NAND Fl h b d NAND Flash-based Storage

NAND Flash-based StorageStorageStorage

Jin-Soo Kim ([email protected])Jin Soo Kim ([email protected])Computer Systems Laboratory

Sungkyunkwan Universityhtt // l kk dhttp://csl.skku.edu

Today’s TopicsToday’s TopicsToday s TopicsToday s TopicsNAND flash memoryy

Flash Translation Layer (FTL)Flash Translation Layer (FTL)

OS implications

2CSE3008: Operating Systems | Fall 2009 | Jin-Soo Kim ([email protected])

Flash Memory CharacteristicsFlash Memory CharacteristicsFlash Memory CharacteristicsFlash Memory CharacteristicsFlash memoryy• Non-volatile, Updateable, High-density• Low cost, Low power consumption, High reliability, p p , g y

Erase-before-write• Read

1 1 1 1 1 1 1 1

• Read• Write or Program: 1 0• Erase: 0 1 1 1 0 1 1 0 1 0

write(program)

• Erase: 0 1

Read faster than write/eraseB lk

1 1 0 1 1 0 1 0

erase

Bulk erase• Erase unit: block

1 1 1 1 1 1 1 1


• Program unit: byte or word (NOR), page (NAND)

NOR FlashNOR FlashNOR FlashNOR FlashNOR flash• Random, direct access

interface• Fast random reads• Slow erase and write• Mainly for code storage

• Intel, Spansion, STMicroSTMicro, ...


NAND FlashNAND FlashNAND FlashNAND FlashNAND flash• I/O mapped access• Smaller cell size• Lower cost• Smaller size erase blocksS a e s e e ase b oc s• Better performance for

erase and write• Mainly for data storage

• Samsung, Toshiba, Hynix


Hynix, ...

NAND Flash ArchitectureNAND Flash ArchitectureNAND Flash ArchitectureNAND Flash Architecture2Gb NAND flash device organizationg


Source: Micron Technology, Inc.

NAND Flash TypesNAND Flash TypesNAND Flash Types NAND Flash Types

SLC NAND1 SLC NAND2SLC NAND(small block)

SLC NAND(large block)

MLC NAND3

Page size (Bytes) 512+16 2,048+64 4,096+128

Pages / Block 32 64 128

Block size 16KB 128KB 512KB

t (read) 15 μs (max) 20 μs (max) 50 μs (max)tR (read) 15 μs (max) 20 μs (max) 50 μs (max)

tPROG (program)200 μs (typ)500 μs (max)

200 μs (typ)700 μs (max)

600 μs (typ)1,200 μs (max)

tBERS (erase)2 ms (typ) 3 ms (max)

1.5 ms (typ)2 ms (max)

3 ms (typ)

NOP 1 (main), 2 (spare) 4 1

Endurance Cycles 100K 100K 10K

ECC(per 512Bytes)

1 bit ECC 2 bits EDC

1 bit ECC2 bits EDC

4 bits ECC5 bits EDC


(per 512Bytes) 2 bits EDC 2 bits EDC 5 bits EDC

1 Samsung K9F1208X0C (512Mb) 2 Samsung K9K8G08U0A (8Gb) 3 Micron Technology Inc.

NAND ApplicationsNAND ApplicationsNAND ApplicationsNAND ApplicationsUniversal Flash Drives (UFDs)( )Flash cards• CompactFlash MMC SD Memory stickCompactFlash, MMC, SD, Memory stick, …

Embedded devicesCell phones MP3 players PMPs PDAs• Cell phones, MP3 players, PMPs, PDAs, Digital TVs, Set-top boxes, Car navigators, …

Hybrid HDDsHybrid HDDsIntel Turbo MemorySSDs (Solid-State Disks)


SSDs (1)SSDs (1)SSDs (1)SSDs (1)HDDs vs. SSDs 1.8” HDD Flash SSD

( 8 4 4 1 )

2.5” HDD Flash SSD(101 70 9 3 )

(78.5x54x4.15mm)

(101x70x9.3mm)

Top BottomTop Bottom


SSDs (2)SSDs (2)SSDs (2)SSDs (2)Feature SSD (Samsung) HDD (Seagate)

Model MMDOE56G5MXP (PM800) ST9500420AS (Momentus 7200.4)

Capacity256GB(16Gb MLC x 128, 8 channels)

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

Form factor2.5”Weight: 84g

2.5”Weight: 110g

Host interfaceSerial ATA‐2 (3.0 Gbps)Host transfer rate: 300MB

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

Power consumptionActive: 0.26WIdle/Standby/Sleep: 0.15W

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

Sequential read: Up to 220 MB/s Power‐on to ready: 4 5 secPerformance

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,Sequential read: 176.73 MB/sSequential write: 159.98 MB/s

/

Sequential read: 86.07 MB/sSequential write: 84.64 MB/s

/256KB for sequential, 4KB for random)

Random read: 10.56 MB/sRandom write: 2.93 MB/s

Random read: 0.61 MB/sRandom write: 1.28 MB/s

Price2 795,000 won 183,840 won


1 Source: http://forums.macrumors.com/showthread.php?t=6585712 Source: http://www.danawa.com (As of Nov. 24, 2009)

NAND Constraints (1)NAND Constraints (1)NAND Constraints (1)NAND Constraints (1)No in-place updatep p• Require sector remapping (or address translation)

Bit errorsBit errors• Require the use of error correction codes (ECC)

Bad blocksBad blocks• Factory-marked & run-time bad blocks

R i b d bl k i• Require bad block remapping

Limited program/erase cycles• < 100K for SLCs• < 10K for MLCs


• Require wear-leveling

NAND Constraints (2)NAND Constraints (2)NAND Constraints (2)NAND Constraints (2)Limited NOP (Number of Programming)( g g)• 1 / sector for most SLCs (4 for 2KB page)• 1 / page for most MLCs/ p g

Sequential page programming• For large block SLCs and MLCs

Pair-page programming in MLCsPair page programming in MLCs• Two pages inside a block are linked together• Performance difference• Performance difference• Interference


FTL (1)FTL (1)FTL (1)FTL (1)Flash cards internals


FTL (2)FTL (2)FTL (2)FTL (2)SSDs internals


Source: Mtron Technology

FTL (3)FTL (3)FTL (3)FTL (3)Flash Translation Layer (FTL)y ( )• A software layer to make NAND flash fully emulate

traditional block devices (e.g., disks).

Why FTL?File System

R d S t W it S t

File System

R d S t W it S ty

• No in-place-update• Bulk erase

Read Sectors Write Sectors

Mismatch!Read Sectors Write Sectors

Read Sectors Write Sectors

Bulk erase

+Device Driver

Read Write Erase

+Device Driver

FTL

++

Flash MemoryFlash Memory

+

Flash MemoryFlash Memory


FTL (4)FTL (4)FTL (4)FTL (4)For performancep• Sector mapping (or address translation)• Garbage collectiong• Interleaving over multiple channels & flash chips• Request schedulingequest sc edu g• Buffer management

For reliabilityFor reliability• Power-off recovery• Wear leveling• Wear-leveling• Bad block management• Error correction code (ECC)


• Error correction code (ECC)

Sector Mapping (1)Sector Mapping (1)Sector Mapping (1)Sector Mapping (1)General page mappingp g pp g• Most flexible• Efficient handling of small writes Data blocks

Logblocksg

• Large memory footprint– One mapping entry per page:

00114414 1’

blocks blocks

LPN 0LPN 0LPN 1

32MB for 32GB MLC (4KB page)– Bitmap for page validity

Per block invalid page counter

101055667

12’2’8’8’1’’1’’

LPN 1LPN 2LPN 2LPN 3LPN 3LPN 4LPN 4LPN 5LPN 5LPN 6LPN 6LPN 7– Per-block invalid page counter

• Sensitive to the amount of reserved blocks

2288111113 2’’

LPN 7LPN 8LPN 8LPN 9LPN 9LPN 10LPN 10LPN 11LPN 11LPN 12LPN 12of reserved blocks

• Performance affected asthe system ages

1515993312

12’12’13’13’9’9’

LPN 13LPN 14LPN 14LPN 15LPN 15


t e syste agesW =

Sector Mapping (2)Sector Mapping (2)Sector Mapping (2)Sector Mapping (2)Naïve block mappingpp g• Each table entry maps one block• Small RAM usage Data blocks

Logblocksg

• Inefficient handling of small writes 0011223

001’1’223

blocks blocks

4455667

LBN 0LBN 0LBN 1LBN 1

4’4’5’5’6’6’7’7’

8899101011

LBN 2LBN 3LBN 3

12121313141415


W =

Sector Mapping (3)Sector Mapping (3)Sector Mapping (3)Sector Mapping (3)Log block scheme [IEEE TOCE 2002]g• A small number of log blocks• 1+ log block(s) per data block Data blocks

Logblocksg ( ) p

• Page mapping for log blocks 0011223

1’1’2’2’1’’1’’2’’

blocks blocks

• Full/partial/switch merge• Switch merge for sequential

4455667

LBN 0LBN 0LBN 1LBN 1Switch merge for sequential

updates 8899101011

LBN 2LBN 3LBN 3

8’8’

• Low log block utilization 12121313141415


W =

Sector Mapping (4)Sector Mapping (4)Sector Mapping (4)Sector Mapping (4)FAST [ACM TECS 2007]• Log blocks shared by all data blocks• Sequential/random log blocks Data blocks

Logblocksq / g

• Improved log block utilization

0011223

blocks blocks

p o ed og b oc ut at o• Increased merge time 44

55667

1’1’2’2’8’8’1’’

LBN 0LBN 0LBN 1LBN 1

8899101011

LBN 2LBN 3LBN 3

2’’2’’12’12’13’13’9’

12121313141415


W =

Sector Mapping (5)Sector Mapping (5)Sector Mapping (5)Sector Mapping (5)Superblock FTL [ACM EMSOFT 2006]p• Superblock = logically adjacent N blocks• A superblock shares log blocks Data blocks

Logblocksp g

• Up to M log blocks per superblock

0011223 1’

blocks blocks

LPN 0LPN 0LPN 1LPN 1LPN 2

• Page mapping within a superblock

4455667

2’2’1’’1’’2’’2’’LSBN 0LSBN 0

LSBN 1LSBN 1

LPN 2LPN 3LPN 3LPN 4LPN 4LPN 5LPN 5LPN 6LPN 6LPN 7LPN 7

• Hot/cold pages separation 8899101011 8’

LPN 8LPN 8LPN 9LPN 9LPN 10LPN 10

• The amount of mappinginformation increased

12121313141415

12’12’13’13’9’9’

LPN 11LPN 12LPN 12LPN 13LPN 13LPN 14LPN 14LPN 15LPN 15


W =

Sector Mapping (6)Sector Mapping (6)Sector Mapping (6)Sector Mapping (6)μ-FTL [ACM EMSOFT 2008]μ• Page mapping• Multiple mapping granularities Data blocks

Logblocksp pp g g

– Based on extents– Reduce the amount of mapping

i f ti

0011223 1’

blocks blocks

information

• Requires more sophisticatedindex structure

4455667

12’2’8’8’1’’1’’

LPN 0, 1LPN 0, 1LPN 1, 1LPN 1, 1LPN 2, 1LPN 2, 1LPN 3, 1LPN 3, 1LPN 4, 4LPN 4, 4LPN 8 1index structure

– μ-Tree is used to store themapping information

8899121213 2’’

LPN 8, 1LPN 9, 1LPN 9, 1LPN 10, 2LPN 10, 2LPN 12, 2LPN 12, 2LPN 14, 2LPN 14, 2

• Tunable memory footprint– Frequently accessed mapping

i f i h d i

10101111141415

12’12’13’13’9’9’


information cached in memoryW =

Performance (1)Performance (1)Performance (1)Performance (1)Simulation environment• 4GB flash memory

– Large block SLC NAND (2KB page, 128KB block)

• FTL schemes– Naïve block mapping– Replacement block– Log block

Superblock– Superblock

• Workload– Trace from PC using NTFSTrace from PC using NTFS


Performance (2)Performance (2)Performance (2)Performance (2)Extra erase and write operationsp• 256 extra blocks

300000

350000

16000000

18000000

200000

250000

10000000

12000000

14000000

Sain

Replacement

Naive

100000

150000

4000000

6000000

8000000Replacement

Logblock

Superblock

0

50000

Erase

0

2000000

Write(GC)


OS Implications (1)OS Implications (1)OS Implications (1)OS Implications (1)NAND flash has different characteristics compared to disks• No seek time• Asymmetric read/write access times• No in-place-updatep p• Good sequential read/sequential write/random read

performance, but bad random write performancep p• Wear-leveling• …

• Traditional operating systems have been optimized for disks What should be changed?


for disks. What should be changed?

OS Implications (2)OS Implications (2)OS Implications (2)OS Implications (2)SSD support in Microsoft Windows 7pp• Turn off “defragmentation” for SSDs• New “TRIM” command

– Remove-on-delete

• Align file system partition with SSD layout• Larger block size proposal (4KB)


SummarySummarySummarySummarySoftware support for NAND flash memory is pp yessential for improving performance & reliability of the systemy y

We need to revisit OS policies andWe need to revisit OS policies and mechanisms which are optimized for disks


Documents

NAND Fl hNAND Flash-bd based Storagecsl.skku.edu/uploads/CSE3008F09/16-flash.pdf · 2011. 2. 14. · SSDs(2)SSDs (2) Feature SSD (Samsung) HDD (Seagate) Model MMDOE56G5MXP (PM800)