PowerEdge customers optimize their server configurations based on their applications and business needs. Multiple factors mustbe taken into consideration to make an informed decision, such as workload, budget, scale,andevenroadmap.Still, when all of the factors are understood, it can be difficultto discern whether the optimized Solid State Drive (SSD) is NVMe, SAS, or SATA.This DfD (Direct from Development) tech note was written to simplify and guide customers in their choice of SSD. We hope customers will find this document to be a valuablereferenceguidewhen it becomes unclear which storage medium is the optimized decision.ThispapercanbeusedasareferenceguidetohelpPowerEdgecustomersmakean informeddecisiononwhichSSDinterfacewillpresumablybringthegreatestvaluein relationtotheirintendedbusinessneedsandgoals.First,let’ssummarizethehistory and architecture around the NVMe, SAS, and SATA SSD interfaces:
The NVMe interface is the newest type of flash storage with the highest performance. ThedrivingarchitecturaldifferentiatorofNVMeisthatitusesthePCIeinterfacebusto connect directly to the CPU and streamline the travel path. This design contrasts with SAS and SATA, which require data to first traverse to an HBA before reaching the CPU. By removing a layer from the stack, the travel path is optimized and produces reduced latency and improved performance. Scalability is also significantly improved, becauseNVMedrivescangobeyondthetraditionalfourlanesbyusinglanesfromthe same “pool” of lanes connected to the CPU. Furthermore, NVMe performance will continually improve as each new generation of the PCIe standard becomes available.
The SASinterfacewas released a fewyears after SATAand introduced new features thatarebeneficialformodernworkloads.InsteadofbuildingupontheATA(Advanced Technology Attachment) standard used in SATA, it serialized the existing parallel SCSI (Small Computer System Interface) standard. SAS cable architecture has four wires within two cables, creating more channels available for moving data and more connectors available for use by other devices. Furthermore, the channels are full duplex, allowing for reads and writes to traverse concurrently. Improved reliability, error reporting, and longer cable lengths were also introduced with SAS. SAS improvements are made to this day, with 24GB/s available soon, so it still remains valuable and relevant within the market.
TheSATAinterfacewasreleasedin2000andisstillcommonlyadoptedwithinmodern servers since it is the most-affordable of the three. It replaced parallel ATA with serial ATA, which resolved various performance and physical limitations at that time. The SATAcablearchitecturehasfourwireswithinonecable—twoforsendingdataandtwo for receiving data. These four channels are half-duplex, so data can only move in one directionatatime.SATAwritespeedsaresufficientforstoringinformation,butitsread speeds are slow compared to more modern interfaces, which limits its application use formodernworkloads.ThelastmajorSATArevisionoccurredin2008,andwillnotsee further advancement in the future.
Table1. Ranking performancemetricsofEnterpriseNVMe,DCNVMe,EnterpriseSAS,ValueSAS,andSATAdrives
Table 1lists key metrics for five storage-drive types most commonly attached to PowerEdge servers: Enterprise NVMe, Data Center (DC) NVMe, Enterprise SAS, Value SAS, and SATA. This comparison helps clarify which storage interface type is most applicable in relation to business needs and goals.
Performance: Performance can be measured in various ways. For this example, Random 4 KiB 70/30 (70% reads, 30% writes) data was comparedand publishedby Dell, with higher IOPS being better. Enterprise NVMe SSDs produce 1.13x moreIOPSthanDCNVMeSSDs.DCNVMeSSDsproduce1.99xmoreIOPSthanEnterpriseSASSSDs.EnterpriseSAS SSDs produce 1.42x more IOPS than Value SAS SSDs. Lastly, Value SAS SSDs produce 2.39x more IOPS than SATA. Figure 1below illustrates the IOPS performance variances on a bar graph for a visual representation:
Figure1.Random4KiB70/30IOPSvariancesforeachstorageinterface
Latency:TheNVMeprotocolreduces thenumber oftouchpoints datamusttravelto(bypassing the HBA)beforereaching the CPU. It also has less overhead, giving itsignificantlylower latency than SAS and SATA. The SAS protocol is full- duplex (as opposed to half-duplex) and offers two channels (as opposed to one) for data to use, giving it over 50% lower latency than SATA.
Price: According to Dell pricing in Q1 2022, SATA SSDs are the least expensive storage interface, at ~0.9x the price of Value SAS SSDs. Value SAS SSDs are ~0.85x the price of DC NVMe SSDs. DC NVMe SSDs are ~0.85x the price of Enterprise SAS SSDs. And Enterprise SAS SSDs are ~0.97x the price of Enterprise NVMe SSDs. Pricing is volatile and these number variances are subject to change at any time.
Performance per price: PowerEdge customers that have not identified which metric is most important for their business goalsshouldstronglyconsiderperformance(IOPS)perprice(dollar)tobeatthetopofthelist.BecauseNVMehassucha significant performance lead over SAS and SATA, it is easily the golden standard for performance per price. DC NVMe SSDshavethebestperformanceperprice,followedcloselybyEnterpriseDCNVMeSSDs,followedbyValueSASSSDs, followed closely by SAS SSDs, followed by SATA SSDs.This tech notegives more performance/price detail.
Scalability: Currently, NVMe shows the greatest promise for wider-scale implementation due to the abundance of lanes thatcanbeavailablewithlow-overhead.However,itcanbeacostlyinvestmentifexistingdatacenterinfrastructures must beupgradedtosupporttheNVMeI/Oprotocol.SASismoreflexible,sinceSASexpandersarecost-effectiveandmostdata centerinfrastructuresalreadyhavetherequiredhardwaretosupportit.However,SASdoesnothavethepotentialtoscale out as aggressively as NVMe. SATA does not scale well with SSDs.
Ongoing development: The NVMe interface has consistent and substantial advancements year-over-year, including updateslikeNVMe2.0b(releasedinJan.2022)andPCIeGen5(releasedonIntelCPUsinNov.2021).TheSASinterface also has regularly cadenced updates, but the impact is marginal, with the exception of upcoming updates like 24Gb/s and 48Gb/s. The SATA interface has no plan to extend capabilities beyond its current limitations.
Assigning these ranks for each storage interface and metric, and explaining why the rank was given, will make it easier to understand which drive type will be the most valuable in relation to business needs and goals.
Every business is unique and will have different requirements for their storagedrives. Factors such as intended workload, businesssize,plantoscale,budget,andsoon,shouldbeconsideredtoconfidentlymakeaninvestmentdecision.Although thisdecisionisultimatelyuptoeachbusiness,wehaveprovidedsomeguidelinesbelowtohelpbusinessesthatarestillon the fence to make an educated choice:
Enterprise NVMe:Businesses that desire maximum performance and have a flexible budget should consider purchasing EnterpriseNVMeSSDs.HeavyworkloadslikeHPCorAIwillimmediatelybenefitfromtheadditionalcachegainedfromthe non-volatile nature of this storage interface. The fast-paced performance growth seen in Enterprise NVMe SSDs will also allow smaller workloads like databases or collaboration to easily keep up with the ever-increasing size of data. Ultimately, becauseEnterpriseNVMeundergoesconsistentvaluablechangeswitheverypassingyear,suchasperformanceincreases and cost reduction/optimization, we recommend futureproofing your data center with it.
DC NVMe: Businesses that desire a budget-conscious NVMe solution, in addition to the greatest value, should consider purchasing DC NVMe SSDs. These drives have the exact same value proposition as stated above for Enterprise NVMe SSDs, but with a sizeable price reduction (0.83x) and performance hit (0.86x). Businesses that want to get the best value will be pleased to know that DC NVMe drives have the best performance-per-price.
Enterprise SAS: Businesses that desire to continue using their existing SCSI-based data center environment and have maximumSASperformance shouldconsiderpurchasingEnterpriseSASSSDs.AlthoughtheEnterpriseSASinterfacedoes notcurrentlyhaveanyrankingleadershipforperformanceorpricing,itisestablishedintheindustryashighlyreliable,cost- effective to scale, and it shows promise for the future, with 24Gb/s available soon and 48Gb/s on the horizon. Enterprise SASSSDswilladequatelyhandlemedium-dutyworkloads,likedatabasesorvirtualization,butwilloperatebestwhenmixed with NVMe SSDs if any heavy-duty workloads are at play.
ValueSAS:Businessesthatdesireabudget-consciousSASsolution shouldconsiderpurchasingValueSASSSDs.These driveshavethesamevalue-propositionasstatedaboveforEnterpriseSASSSDs,butwithbotha sizeablepricereduction (0.73x) and performance hit (0.71x). For this reason, it actually has a slightly lower performance-per-price than Enterprise SAS,andthereforeismoreofa“value”playwhencomparedagainstSATA.Thisstorageinterfacehasapurposeforexisting though,assmall-to-mediumbusinesseswithasmallerbudgetcanleveragethislower-costsolutionwhilestillreceivingthe many benefits of the SAS interface.
SATA:Businessesthatdesirethelowestprice storageinterfaceshouldconsiderpurchasingSATASSDs.However,caution shouldbeappliedwiththisstatement,asthereiscurrentlynoothervaluepropositionforSATASSDs,andthepricegapfor theseflashstorageinterfaceshasbeenshrinkingovertime,whichmayeventuallyremoveanyvalidreasonfortheexistence of SATA. With that being said, SATA is currently still a solid choice for light workloads that are not read-heavy.
ThestoryofcompetingNVMe,SAS,andSATAstorageinterfacesisstillbeingwritten.Fiveplusyearsago,analystsmade the argument that although NVMe has superior performance, its high-cost warranted SAS the title of ‘best value for years tocome’.Whatweseetodayisarapidlyshrinkingpricegapforalloftheseinterfaces.WeobservethatSATAperformance hasfallenfarbehindSAS,andveryfarbehindNVMe,withnoplantoimproveitscurrentstate.WealsoseeNVMeoptimizing its performance and price-point to yield more market share every year. Most importantly, we expect rapid growth in the industry adoption ofheavier workloads and ever-increasing datarequirements. Both storage drive and industry trends inclineus to believe that the best option for any business desiring to build a future-proofed datacenter would be to begin making the investment in NVMe storage. However, the remaining types of storage still hold value for varying use cases, and it is the customer’s choice to decide which storage type is best for their business goals. We hope this guide has helped that decision become more apparent.