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©2019WesternDigitalCorporationoritsaffiliates.Allrightsreserved. 06.03.19
From Open-Channel SSDs to Zoned Namespaces
MatiasBjørlingDirector,Solid-StateSystemSoftware
23th January2019
06.03.19©2019WesternDigitalCorporationoritsaffiliates.Allrightsreserved. 2
This presentation contains forward-looking statements that involve risks and uncertainties, including, but not limited to, statements regarding our solid-state technologies, product development efforts, software development and potential contributions, growth opportunities, and demand and markettrends. Forward-looking statements should not be read as a guarantee of future performance or results, and will not necessarily be accurate indications ofthe times at, or by, which such performance or results will be achieved, if at all. Forward-looking statements are subject to risks and uncertainties thatcould cause actual performance or results to differ materially from those expressed in or suggested by the forward-looking statements.
Key risks and uncertainties include volatility in global economic conditions, business conditions and growth in the storage ecosystem, impact ofcompetitive products and pricing, market acceptance and cost of commodity materials and specialized product components, actions by competitors,unexpected advances in competing technologies, difficulties or delays in manufacturing, and other risks and uncertainties listed in the company’s filingswith the Securities and Exchange Commission (the “SEC”) and available on the SEC’s website at www.sec.gov, including our most recently filed periodicreport, to which your attention is directed. We do not undertake any obligation to publicly update or revise any forward-looking statement, whether as aresult of new information, future developments or otherwise, except as required by law.
Forward-Looking StatementsSafeHarbor|Disclaimers
06.03.19©2019WesternDigitalCorporationoritsaffiliates.Allrightsreserved. 3
Ubiquitous WorkloadsEfficiency of the Cloud requires many different workloads to a single SSD
3
Databases Sensors Analytics Virtualization Video
Solid-StateDrive
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Solid State Drive Internals
LogicaltoPhysicalTranslationMap
HighlyParallelArchitecture
Wear-Leveling GarbageCollection
BadBlockManagement MediaErrorHandling …
Die0
Die1
Die2
Die3
Die0
Die1
Die2
Die3
Die0
Die1
Die2
Die3
Die0
Die1
Die2
Die3
MediaInterfaceController
Read/WriteHostInterface(NVMe)
Read(50-100us)
Write(1-10ms)
Erase(3-15ms)
Read/Program/Erase
• NANDRead/Program/Erase
• HighlyParallelArchitecture– TensofDies
• NANDAccessLatencies• TranslationLayer– LogicaltoPhysicalTranslationLayer– Wear-leveling– GarbageCollection– Badblockmanagement– Mediaerrorhandling– Etc.
• Read/Write/Erase->Read/Write
SolidStateDrive
©2018WesternDigitalCorporationoritsaffiliates.Allrightsreserved.
06.03.19©2019WesternDigitalCorporationoritsaffiliates.Allrightsreserved. 5
Open-Channel Concepts
• Chunks– WritesequentiallywithinanLBArange– Requiresresetforrewrites– BorrowsfromHDD’sSMRspecification(ZAC/ZBC)
– OptimizedforSSDphysicalconstraints• Alignwritestomedialayout
• ParallelUnits– HostcandirectI/Ostoseparateworkloads– Stripesacrosssingleormultipledies.– Theparallelunitsinheritsthethroughputandlatencycharacteristicsoftheunderlyingmedia
– SimilarconcepttoI/ODeterminisminNVMe
Chunks & Parallel Units
Application-1 Application-2 Application-3
SSDFirmware
FlashFlash
Application-1FTL-1
Application-2FTL-2
Application-3FTL3
SSDFirmware
Chunk0 Chunk1 Chunk2 Chunk3 ChunkX
DiskLBArangedividedinchunks
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Open-Channel SSDs
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I/O Isolation Predictable Latency Data Placement &I/O Scheduling
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Open-Channel SSDsInterface Adoption
Open-ChannelSSDarchitecturesarebeingadoptedbymajorhyper-scalers
ConceptsreadytobepartoftheNVMestandardspecification
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NVMe ApproachDrivefeaturesintoNVMewhichaddresskeyOCSSDusecases
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• ExplicitProvisioningofDeviceTopology
• BuildonIODeterminism
EnduranceGroupMgmt(e.g.ParallelUnits)ZonedNamespaces(e.g.Chunks)
Today’stalk
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Zoned Namespaces (ZNS)
• TechnicalProposalintheNVMeworkinggroup
• Standardizeszoneinterfaceasanapproachto:– Reducedevice-sidewriteamplification– Reduceover-provisioning• “Notethatexcessiveover-provisioningissimilartoearlyreplacement-- inbothcasesyoubuymoredevices.”
- MarkCallaghan,Facebook– ReduceDRAMinSSDs• HighestcostafterNANDitself
– Improvelatencyoutliersandthroughput• Lessdevice-sidedatamovement• Tailatscale
– Enablesoftwareeco-system.• Everyonebenefitsfromimprovements!
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Zoned Namespaces similar to ZBC/ZAC for SMR HDDs•Storagecapacityisdividedintozones•Eachzoneiswrittensequentially• InterfaceoptimizedforSSDs
– Alignwithmediacharacteristics• Zonesizealignedtomedia(E.g.,NANDblocksizes)• Zonecapacityalignedtophysicalmediasizes
– ReduceNANDmediaerasecycles(Writeamp.)
Zone0 Zone1 Zone2 Zone3 ZoneX
Writepointerposition
DiskLBArangedividedinzones
Writecommandsadvancethewrite
pointer
Resetwritepointercommandsrewindthewritepointer
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Zone Information
• ZoneState– Empty,ImplicitlyOpened,ExplicitlyOpened,Closed,Full,ReadOnly,Offline
– Empty->Open->Full-> Empty->….
• ZoneReset– Full->Empty
• ZoneSize&ZoneCapacity– ZoneSizeisfixed– ZoneCapacityisthewriteableareawithinazone
ZoneCapacity(E.g.,500MB)
ZoneSize(e.g.,512MB)
ZoneStartLBA
ZoneXZoneX- 1 ZoneX+1
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Zone Append
• Lowscalabilityonmultiplewriterstoazone– WriteQueueDepthperZone=1– IOPS:80Kvs880KonQemuand300Kvs1400Konmetal
• ZAC/ZBCrequiresstrictwriteordering
• Limitswriteperformanceandincreaseshostoverhead
• Bigchallengewithsoftwareeco-system,HBAs,etc.
• IntroducingZoneAppend• Appenddatatoazonewithoutdefiningoffset• Drivereturnswheredatawaswritteninthezone
-100 100300500700900
110013001500
1 2 3 4
KIOPS
NumberofJobs
QEMU(i7-6700K,4K,QD1,RW,libaio)
1Zone 4Zones ZoneAppend/NoZones
-100 100300500700900
110013001500
1 2 3 4
KIOPS
NumberofJobs
Metal(i7-6700K,4K,QD1,RW,libaio)
1Zone 4Zones ZoneAppend/NoZones
ZoneLockContention
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Zone Write Example3x Writes (4K, 8K, 16K) – Queue Depth = 1
4K Write0
8K Write1
16K Write2
WPWP WP WP
Zone
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Zone Append Example3x Writes (4K, 8K, 16K) – Queue Depth = 3
4K Write0
8K Write1
16K Write2
WPWP WP WP
Zone
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ZNS: Synergy w/ ZAC/ZBC software ecosystem
• ExistingZAC/ZBC-awarefilesystems&devicemappers“justwork”– FewchangestosupporttoZNS
• ReuseexistingworkalreadyappliedwithforZAC/ZBChard-drives(SMR)
• Integratedirectlywithfile-systems– Nohost-sideFTL– No1GBDRAMper1TBMediarequirement– BetterutilizationofSSD
• Codeisalreadyinproductionathyper-scalersandavailableintheLinuxeco-system.
06.03.19
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SMRHDDZBC/ZAC
ZNSSSD
Applicationslibzbc
LogicalBlockDevice(dm-zoned)
File-SystemwithSMRSupport
(f2fs,btrfs)
SCSI/ATA
RegularFile-Systems(xfs)
UserSpace
LinuxKernel
BlockLayer
NVMe
*=EnhanceddatapathsforSMRdrives
util-linux fio
blktests
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Mature Software Stack
• User-spacelibraries– Libzbd– Nvme-cli– Blktests– Util-linux(blkzone)– fio– libzns
• Kernel-spacelibraries– NVMesupportforZones– XFS,Btrfs,F2FS,dm-zoned,etc…
• QemuwithZNSsupport
ZNS to use existing storage stack
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ZBC State Model
• States(Empty,ImplicitlyOpened,ExplicitlyOpened,Full,Offline)
• Eachzone– Size– Capacity– WritePointer– Andotherfields
• ZoneManagementcommand– ZMOpen,ZMClose,ZMReset,ZMFinish
©2019WesternDigitalCorporationoritsaffiliates.Allrightsreserved. 06.03.19
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