Seagate's Contribution to Legacy File Systems

SMR in Linux Systems

Adrian Palmer, Drive Development Engineering

2

SEAGATE combines

DIFFERENT TECHNOLOGIES in new ways

to SOLVE customer data storage CHALLENGES

3Data adapted from ASTC Technology Roadmap (http://www.idema.org/?page_id=5868)

Shingled Magnetic Recording (SMR)Areal density growth curve – lowest cost/GB

0.1

1

10

2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024

TB/in^2

BPMR

(Bit Patterned Magnetic Recording)

HDMR

with BPMRBPMR

with SMRHAMR

with SMR

SMR

PMR

PMR (Perpendicular Magnetic Recording)

SMR

(Shingle Magnetic Recording)

HAMR

(Heat Assisted Magnetic Recording)

4Image: Wood, R.; Williams, Mason; Kavcic, A.; Miles, Jim, "The Feasibility of Magnetic Recording at 10 Terabits Per Square Inch on Conventional Media," Magnetics, IEEE Transactions on , vol.45, no.2, pp.917,923, Feb. 2009

Shingled Magnetic Recording (SMR)Forward-write only: Radial AND Rotational

Drive Managed (DM)

Mimics Traditional drives

Backwards compatible

Direct Replacement for conventional drives in conventional apps

Host Managed (HM)

Not backwards compatible

Host required to manage data ordering for performance mitigation

Extensions required in ATA and SCSI command sets

Host Aware (HA)

Combination of DM and HM.

Backwards compatible / Able to use extensions in ATA and SCSI

SMR Drive Types

“

“

6

Host Aware

Regular SD drive

FS benefits from

knowledge of media

layout

Drive Managed

No change: regular

SD drive

Host Managed

Requires new

device & FS

Host Aware:

Capacity gains like

Drive Managed

Performance like

Conventional

Drive Managed –

Compatibility for

Today

Host Aware –

Performance for

Tomorrow

Benefits

Provides continued growth in Areal Density.

Enables lower cost/GB disc drives

Base of new technologies – HAMR

Support Readiness

ZBC/ZAC specifications are nearing completion

T10/T13 committees work actively progressing

Availability

Millions of DM drives shipped!

Seagate’s 8TB Archive HDD v2 drive is SMR

DM in production, HA forthcoming

SMR – Can we avoid it?

ZBC: Zoned Block Commands

ZAC: Zoned –device ATA Commands

8

• Inspired by SMR. Applicable to any media

• Separates media into bounded zones

• Write Pointer Zones

• Sequential write only for Host Managed (restrictive)

• Sequential write preferred for Host Aware (permissive)

• New common ATA/SCSI commands

• REPORT ZONES

• RESET WRITE POINTER

• OPEN/CLOSE/FINISH ZONE

• Requires communication with FS beyond simple Read/Write

ZAC/ZBC Standards

9

• Optimally Directed Writes – efficient

streams

• Excellent Reads – streaming

• File defragmentation

• Metadata handling

• Backwards compatibility

• Provide reference design for other

file systems

• Forward-write only

• CoW requirement

• Zone aware (ZAC/ZBC)

• Boundaries

• New Commands

• REPORT_ZONES

• RESET_WRITE_POINTER

• OPEN/CLOSE/FINISH ZONE

• New algorithms

• Defragmentation

SMR Friendly File System

Requirements Goals

10

SMRFS -EXT4

• Minimal architecture changes; only rearrangement of existing data

• Popular in commercial storage applications

• Build upon strengths

• Default FS of many distros

Popular FS Stability

Compatible on-disk format

Market Acceptance

12

1. cmd line arguments

2. internal handling changes

3. kernel stack changes

4. IOCTL integrations

5. Algorithm enhancements

6. Utility updates

7. Host Managed Compliance

EXT4 SMRFFS Project Scope Steps

Proposed Stages

Disk

SCSI

EXT4

Specify mkfs Options for HAv1

Kern

el S

tack

v3

v2v2

v2

Internal

changes

v2

Kernel Integrationv4

Garbage Collectionv5

Enforce Host Managedv7Utilities

v6

v1

v2

v3

v4

v5

v6

v7

13

V3 - Kernel Stack Changes, V4 Kernel Integration

Proposed Stack Changes

Disk

AHCI

ATA

S-A-T

SCSI

O_Direct

VFS

I/O Scheduler

Page Cache

EXT4

VFS Examine/Enforce

I/O Ordering

IOCTL√

√

14Seagate Confidential

State of project

We’ve done … • Laid out design, made prototypes

Discussion at LSF…• Consensus of key developers

We’ve got to do …• A lot of work – in a short time

And we need community help!• Ask how to contribute and how to get sample drives at our booth!

• Contact us after Vault at adrian.palmer@seagate.com or timothy.r.feldman@seagate.com

15

For Drive Managed SMR

File System Parameters Influence Performance

6080

100120140160180200

ext4

ext4

fle

x_

bg

ext4

dm

-co

w

zfs

btr

fs

ext4

ext4

fle

x_

bg

ext4

dm

-co

w

zfs

btr

fs

ext4

ext4

fle

x_

bg

ext4

dm

-co

w

zfs

btr

fs

ext4

ext4

fle

x_

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ext4

dm

-cow

zfs

btr

fs

Mimic OS Load Mimic DVD Download 5meg files Deep Dir 1meg files Deep Dir

Th

rou

gh

pu

t -

MB

/s

Drive Managed SMR - Performance by FS Parameters, for different Workloads

driveA

driveB

driveC

Re-arranging file system parameters for CoW to enforce forward-write-

only improves performance of a DM-SMR-enabled system

Q&A

Thank You!

Attendees and Partners