optimizing ssd architecture for client workloads

Santa Clara, CA—August 2016 1

Optimizing SSD Architecture for

Client Workloads

Elad Baram

Sr. Director, SSD Product Management


Agenda

Workloads and Locality Concept

SSD Architecture and Performance Enablers

Locality of Workloads Study

Recommendations


Workload Key Attributes

Three key characteristics of workloads

• Bandwidth over time

– MB/s

• Transactions over time

– IOPs

• Locality over time

– The degree of repetitiveness in host logical addresses accesses

– Defined as % of hit/miss ratio relative to a given Logical to Physical (L2P) mapping

table size (i.e., workload with 4GB locality means a device with 4GB addresses

mapped table will have 90% hit rate)


Locality Overview

SSD architectures use different sizes for L2P mapping tables

• From small tables in DRAM-less SSDs, to full 1:1 4KB mapping with DRAM

L2P table size is a cost/performance optimization decision

A study done to quantify impact of L2P table sizes on SSD performance

in different applications environments

• Study the locality of real-life client workloads

• Locality of benchmarks

• Understand optimal cost/performance

Main outcome - client workloads are highly localized


SSD Block Diagram

Host

HMB

CPU/LogicHost

Interface

Flash

Interface

DDR

NAND

SSD


Host

HMB

CPU/LogicHost

Interface

Flash

Interface

DDR

NAND

SSD

Factors limiting performance

SSD Block DiagramSequential Read/Write Enablers


Host

HMB

CPU/Logic/FWHost

Interface

Flash

Interface

DDR

NAND

SSD

Factors limiting performance

SSD Block DiagramIOPS Enablers


Host

HMB

CPU/LogicHost

Interface

Flash

Interface

DDR

NAND

DDR usage

• L2P (logical-to-physical) translation tables (>90% of space)

• Buffering

• Code space

SSD

SSD Block Diagram – What is Enabled by DDR?


L2P Table Size Impact on SSDs Performance

RR IOPS

Workload LBA Range

4KB 1:1 L2P Mapping

1GB 128GB

Maximum

system

IOPS

256GB

‘Control read’* penalty

L2P table size does NOT define

the maximum performance

• Those are defined by NAND, CPU,

FW efficiencies

L2P table size defines the envelope

in which IOPS can be maintained

PCMark

Vantage

Crystal

Diskmark

* Control read is an internal read command issued by SSD to bring meta-data, such as mapping table page


Deeper look into workloads


Cre

ate

file

Sequential Read multiple IOs, threads

Random Read multiple IOs, threads

Random Read Single IO, thread

Sequential

Write Single IO,

thread

Sequential

Write multiple

IOs, threads

Random Write multiple IOs,

threads

Random Write Single IO, thread

Sequential Read Single IO, thread

Synthetic Benchmark—Crystal Disk Mark

Read

Write

Logical address accessed by the host over time

CDM accesses ~1GB logical range


Synthetic Benchmark—Crystal Disk Mark

Sequential Read

Multiple threads

Random Read

Multiple threads

Sequential Read

Single thread

Random Read

Single thread

Sequential Write

Multiple threads

Random Write

Multiple threads

Sequential Write

Single thread

Random Write

Single thread

Read

Write


Windows

Defender

Gaming Importing Pictures Windows Startup Windows Media Center Adding music

to Windows

Media

Video Editing Applications

Loading

PCMark Vantage Workload Read

Write

Different logical access pattern for each use case

Bandwidth & IOPS are bursty


3 Days 6 Days 8 Days

Real User Workload (10 Days) Read

Write

Broad address spread

Bandwidth & IOPS are bursty


Real User Workload

Read

Write

How can you translate access pattern raw data into insightful design decisions?


Locality of Client SSD Workloads


Research Flow

L2P Tables

Read

request

Is requested

address stored

in table?

Evacuate space

(defined policy)

Fetch new

address

(miss)

Continue

(hit)

Command Trace

Fed into simulator

Yes

No

NAND NAND NAND NAND


4MB L2P Table Size Drives Higher than 90% Hit Rates

0

10

20

30

40

50

60

70

80

90

100

5

38

42

79

90

119

122

144

196

310

429

435

450

510

583

589

608

615

106

7

196

8

213

7

224

7

277

3

364

3

364

8

366

5

376

8

379

6

380

1

381

0

381

7

462

2

494

0

495

8

513

5

543

3

543

6

548

5

557

9

558

3

559

0

559

9

628

5

HIT

RA

TE

(%

)

TIME

0.5MB

4MB

512MB

L2P Table Size

Source: SanDisk Technical Marketing research lab; Simulation results based on traces from: Intel Skylake, Intel Core i7, 8GB RAM, Microsoft Windows 10 Pro x64 Platform

SYSMark 2014 Hit Rates for Various L2P Table Sizes


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

HIT

RA

TE

(%

)

TIME

0.5MB

4MB

256MB

4MB L2P Table Size Drives Higher than 90% Hit Rates

Trace period 21 days.


Real User (Developer Profile) Hit Rates for Various L2P Table Sizes


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

512MB 256MB 128MB 64MB 32MB 16MB 8MB 4MB 2MB 1MB 512KB 32KB

HIT

RA

TE

(%

)

L2P SIZE

PCMARK VANTAGE

PCMark 8

SYSMark 2014

MobileMark 2014

Copy Files and Folders 11.6GB

Corporate Profile

Developer Profile

4GB Logical Range Coverage (4MB L2P Table Size) Provides

95%+ Average Hit Rate for Benchmarks and Workloads


Hit Rates in L2P Table Sizes for Various Workloads



IOMeter 40GB LBA range, SW SR RW RR

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

512MB 256MB 128MB 64MB 32MB 16MB 8MB 4MB 2MB 1MB 512KB 32KB

HIT

RA

TE

(%

)

L2P SIZE

PCMARK VANTAGE

PCMark 8

SYSMark 2014

MobileMark 2014

Copy Files and Folders 11.6GB

Corporate Profile

Developer Profile

IOMeter

Synthetic workload

is not a reflection

of typical client

Hit Rates in L2P Table Sizes for Various Workloads

Locality of Workloads

Locality represents the required L2P table size that enables 90% hit rate for read pattern

1

10

100

1,000

1 10 100 1,000

Tota

l Rea

ds

(GB

)

L2P Size (MB)

CDM 1GB CDM 4GB

PCMark 8

Copy Files and Folders

IOMeter Full Range

PCMark Vantage

Office Productivity

Media Creation

Additional Optimizations for Client SSD

• Eliminating DRAM component enables

• Higher density on single side M.2

• Power savings

• Cost optimization

M.2 2280

NAND

DDR

CTRL

NAND NAND NAND

Controller

M.2 2280

NAND NAND NAND NANDDDRX


Summary

Client workloads are bursty – SLC caching is appropriate

Client workloads are highly localized

• Windows productivity applications

• PCMark / Sysmark are good representatives for locality of user applications

• Full range logical test area is not a reflection of client workloads

A 4GB logical mapping range is the optimal cost/performance point

optimizing ssd architecture for client workloads

Technology