Blog Feed Post

Effects Of Linux IO Scheduler On SSD Performance

This blog begins a series of blogs which present test results of testing performed at VeloBit to investigate the effects of different Linux IO scheduler algorithms on IO bandwidth when SSDs are operated in a simulated enterprise environment. This series of blogs is similar to the series we previously presented documenting IO bandwidth vs. read/write ratio. This first blog will document the test set up and procedures and present the results from one tested device. In following weeks, I will refer the reader back to this blog for test set up and procedure information and simply present the results for another device. After presenting results of a particular week, I will make observations as appropriate.

Test Motivation and Procedure
For this group of tests, we wanted to focus on the effect of the selected Linux IO scheduler on the IO bandwidth performance of the SSD. An IO scheduler controls the way the Linux kernel commits reads and writes to disk (or SSD). There are several different schedulers supported by Linux; each one having particular advantages with respect to particular IO workload. The Linux kernel supports 4 different IO schedulers:
  • No-op scheduler (NOOP)
  • Complete fair queueing scheduler (cfq)
  • Deadline scheduler
  • Anticipatory scheduler

However, these schedulers are designed for HDD.  For SSD installations, an IO scheduler may not be required since each SSD has its own specific scheduler inside the SSD controller.

We tested 5 different SSDs from 4 different manufactures. Some are SATA devices and some are PCI-E devices. We used a Linux based system running with the Intel Open Storage Toolkit, a tool similar to Iometer that runs on Linux. The Open Storage Toolkit generates synthesized workloads with various sizes and queue lengths and also provides monitoring and IO tracing capabilities. We also used another set of tools available in Linux, blktrace and blkparse that intercept all block-level requests. The idea was to observe IO bandwidth under operating conditions.

So for this test, we ran identical test suite for each IO scheduler algorithm listed above and observed IO bandwidth. We used 6 different IO request sizes for each scheduler: 1 KB, 4 KB, 16 KB, 64 KB, 128 KB and 256 KB. We ran 4 different sets of these tests based on IO type: random read, sequential read, random write and sequential write.

General Observations
Overall, for the 5 devices tested, we found that none are very sensitive to different IO scheduler algorithms and no consistent results were observed across all devices. However, there are some interesting observations to be made. The NOOP scheduler is generally believed to be the best used with SSDs because SSDs do not depend on mechanical movement to access data. Such non-mechanical devices do not require re-ordering of multiple I/O requests (grouping together I/O requests that are physically close together on the disk), thereby reducing average seek time and the variability of I/O service time. These test results show that the NOOP scheduler is not necessarily the best for all devices.

Test SSD: 250 GB OCZ Z Drive PCI-E based SSD

Figure 1: IO Scheduler Bandwidth for OCZ Z Drive: a) random read b) sequential read

Figure 2: IO Scheduler Bandwidth for OCZ Z Drive: a) random write b) sequential write

Figures 1 and 2 shows the results of OCZ Z Drive. Relative to the other schedulers, the anticipatory scheduler performs poorly for the random read workload.  The reason is that this scheduler tries to avoid disk seek operations by waiting a very short time for another read that is physically located near the current read request. This introduces some overhead for SSD because even a short waiting time for SSD is not necessary. The same anticipatory scheduler does not affect write performance because it only executes the “wait” during read requests. For sequential read, the anticipatory scheduler also does not have any negative effect because the next read request it is waiting for is physically close to the current read request, so its performance is similar to the other three schedulers.

Also note that for random workloads (both read and write), the NOOP scheduler performs the worst when the request size is big (128 KB and 256 KB). This is because NOOP puts all requests into a simple FIFO queue, which means that requests must be processed in order and new requests cannot be processed unit one is completed.  This is different than schedulers which are multi-queue (complete fair queueing , deadline or anticipatory).  These schedulers can process requests in parallel.

Come back next week for results and observations on another SSD.

Read the original blog entry...

More Stories By Peter Velikin

Peter Velikin has 12 years of experience creating new markets and commercializing products in multiple high tech industries. Prior to VeloBit, he was VP Marketing at Zmags, a SaaS-based digital content platform for e-commerce and mobile devices, where he managed all aspects of marketing, product management, and business development. Prior to that, Peter was Director of Product and Market Strategy at PTC, responsible for PTC’s publishing, content management, and services solutions. Prior to PTC, Peter was at EMC Corporation, where he held roles in product management, business development, and engineering program management.

Peter has an MS in Electrical Engineering from Boston University and an MBA from Harvard Business School.

Latest Stories
DevOps promotes continuous improvement through a culture of collaboration. But in real terms, how do you: Integrate activities across diverse teams and services? Make objective decisions with system-wide visibility? Use feedback loops to enable learning and improvement? With technology insights and real-world examples, in his general session at @DevOpsSummit, at 21st Cloud Expo, Andi Mann, Chief Technology Advocate at Splunk, explored how leading organizations use data-driven DevOps to close th...
"Digital transformation - what we knew about it in the past has been redefined. Automation is going to play such a huge role in that because the culture, the technology, and the business operations are being shifted now," stated Brian Boeggeman, VP of Alliances & Partnerships at Ayehu, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
The past few years have brought a sea change in the way applications are architected, developed, and consumed—increasing both the complexity of testing and the business impact of software failures. How can software testing professionals keep pace with modern application delivery, given the trends that impact both architectures (cloud, microservices, and APIs) and processes (DevOps, agile, and continuous delivery)? This is where continuous testing comes in. D
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"WineSOFT is a software company making proxy server software, which is widely used in the telecommunication industry or the content delivery networks or e-commerce," explained Jonathan Ahn, COO of WineSOFT, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
Mobile device usage has increased exponentially during the past several years, as consumers rely on handhelds for everything from news and weather to banking and purchases. What can we expect in the next few years? The way in which we interact with our devices will fundamentally change, as businesses leverage Artificial Intelligence. We already see this taking shape as businesses leverage AI for cost savings and customer responsiveness. This trend will continue, as AI is used for more sophistica...
There is a huge demand for responsive, real-time mobile and web experiences, but current architectural patterns do not easily accommodate applications that respond to events in real time. Common solutions using message queues or HTTP long-polling quickly lead to resiliency, scalability and development velocity challenges. In his session at 21st Cloud Expo, Ryland Degnan, a Senior Software Engineer on the Netflix Edge Platform team, will discuss how by leveraging a reactive stream-based protocol,...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
Sanjeev Sharma Joins June 5-7, 2018 @DevOpsSummit at @Cloud Expo New York Faculty. Sanjeev Sharma is an internationally known DevOps and Cloud Transformation thought leader, technology executive, and author. Sanjeev's industry experience includes tenures as CTO, Technical Sales leader, and Cloud Architect leader. As an IBM Distinguished Engineer, Sanjeev is recognized at the highest levels of IBM's core of technical leaders.
Product connectivity goes hand and hand these days with increased use of personal data. New IoT devices are becoming more personalized than ever before. In his session at 22nd Cloud Expo | DXWorld Expo, Nicolas Fierro, CEO of MIMIR Blockchain Solutions, will discuss how in order to protect your data and privacy, IoT applications need to embrace Blockchain technology for a new level of product security never before seen - or needed.
The 22nd International Cloud Expo | 1st DXWorld Expo has announced that its Call for Papers is open. Cloud Expo | DXWorld Expo, to be held June 5-7, 2018, at the Javits Center in New York, NY, brings together Cloud Computing, Digital Transformation, Big Data, Internet of Things, DevOps, Machine Learning and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding busin...
Digital transformation is about embracing digital technologies into a company's culture to better connect with its customers, automate processes, create better tools, enter new markets, etc. Such a transformation requires continuous orchestration across teams and an environment based on open collaboration and daily experiments. In his session at 21st Cloud Expo, Alex Casalboni, Technical (Cloud) Evangelist at Cloud Academy, explored and discussed the most urgent unsolved challenges to achieve f...
SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...
Digital Transformation (DX) is not a "one-size-fits all" strategy. Each organization needs to develop its own unique, long-term DX plan. It must do so by realizing that we now live in a data-driven age, and that technologies such as Cloud Computing, Big Data, the IoT, Cognitive Computing, and Blockchain are only tools. In her general session at 21st Cloud Expo, Rebecca Wanta explained how the strategy must focus on DX and include a commitment from top management to create great IT jobs, monitor ...