Welcome!

Containers Expo Blog Authors: Jamie Madison, Dalibor Siroky, PagerDuty Blog, Stackify Blog, Matt Lonstine

Related Topics: Containers Expo Blog, @CloudExpo

Containers Expo Blog: Article

Why Your Storage Isn't Always to Blame

CRC Errors, Code Violation Errors, Class 3 Discards & Loss of Sync

Storage is often automatically pinpointed as the source of all problems. From System Admins, DBAs, Network guys to Application owners, all are quickly ready to point the figure at SAN Storage given the slightest hint of any performance degradation. Not really surprising though, considering it's the common denominator amongst all silos. On the receiving end of this barrage of accusation is the SAN Storage team, who are then subjected to hours of troubleshooting only to prove that their Storage wasn't responsible. On this circle goes until there reaches a point when the Storage team are faced with a problem that they can't absolve themselves of blame, even though they know the Storage is working completely fine. With array-based management tools still severely lacking in their ability to pinpoint and solve storage network related problems and with server based tools doing exactly that i.e. looking at the server, there really is little if not nothing available to prove that the cause of latency is a slow draining device such as a flapping HBA, damaged cable or failing SFP. Herein lies the biggest paradox in that 99% of the time when unidentifiable SAN performance problems do occur, they are usually linked to trivial issues such as a failing SFP.  In a 10,000 port environment, the million dollar question is ‘where do you begin to look for such a miniscule needle in such a gargantuan haystack?'

To solve this dilemma it's imperative to know what to look for and have the right tools to find them, enabling your SAN storage environment to be a proactive and not a reactive fire-fighting / troubleshooting circus. So what are some of the metrics and signs that should be looked for when the Storage array, application team and servers all report everything as fine yet you still find yourself embroiled in performance problems?

Firstly to understand the context of these metrics / signs and the make up of FC transmissions, let's use the analogy of a conversation. Firstly the Frames would be considered the words, the Sequences the sentences and an Exchange the conversation that they are all part of. With that premise it is important to first address the most basic of physical layer problems, namely Code Violation Errors. Code Violation Errors are the consequence of bit errors caused by corruption that occur in the sequence - i.e. any character corruption. A typical cause of this would be a failing HBA that would eventually start to suffer from optic degradation prior to its complete failure. I also recently experienced at one site Code Violation Errors when several SAN ports had been left enabled after their servers had been decommissioned. Some might think what's the problem if they have nothing connected to them? In fact this scenario was creating millions of Code Violation Errors causing a CPU overhead on the SAN switch and subsequent degradation. With mission critical applications connected to the same SAN switch, performance problems became rife and without the identification of the Code Violation Errors could have led to weeks of troubleshooting with no success.

The build up of Code Violation Errors become even more troublesome as they eventually lead to what is referred to as a Loss of Sync. A Loss of Sync is usually indicative of incompatible speeds between points and again this is typical of optic degradation in the SAN infrastructure. For example if an SFP is failing, its optic signal will degrade and hence will not be at for example the 4Gbps it's set at. Case point: a transmitting device such as a HBA is set at 4Gbps while the receiving end i.e. the SFP (unbeknownst to the end user) has degraded down to 1Gbps. Severe performance problems will occur as the two points constantly struggle with their incompatible speeds. Hence it's an imperative to be alerted of any Loss of Sync as ultimately they are also an indication of an imminent Loss of Signal i.e. when the HBA or SFP are flapping and are about to fail. This leads to the nightmare scenario of an unplanned path failure in your SAN storage environment and worse still a possible outage if failover cannot occur.

One of the biggest culprits and a sure-fire hit to resolving performance problems is to look for what are termed CRC errors. CRC Errors usually indicate some kind of physical problem within the FC link and are indicative of code violation errors that have led to consequent corruption inside the FC data frame. Usually caused by a flapping SFP or a very old / bent / damaged cable, once CRC errors are acknowledged by the receiver, the receiver would reject the request leaving the Frame having to be resent. For example as an analogy imagine a newspaper delivery boy, who while cycling to his destination loses some of the pages of the paper prior to delivery. Upon delivery the receiver would request for the newspaper to be redelivered with the missing pages. This would entail the delivery boy having to cycle back to find the missing pages and bring back the newspaper as a whole. In the context of a CRC error a Frame that should typically take only a few milliseconds to deliver could take up to 60 seconds in being rejected and resent. Such response times can be catastrophic to a mission critical application and it's underlying business. By gaining an insight into CRC errors and their root cause one can immediately pinpoint which bent cable or old SFP is responsible and proactively replace them long before they start to cause poor application response times or even worse a loss to your business.

The other FC SAN gremlin is what is termed a Class 3 discard. Of the various services of data transport defined by the Fibre Channel ANSI Standard, the most commonly used is Class 3. Ideal for high throughput, Class-3 is essentially a datagram service based on frame switching and is a connectionless service. Class 3's main advantage comes from not giving an acknowledgement that a frame has been rejected or busied by a destination device or Fabric. The benefits of this are that it firstly significantly reduces the overhead on the transmitting device and secondly allows for more bandwidth availability for transmission which would otherwise be reduced. Furthermore the lack of acknowledgements removes the potential delays between devices caused by round-trips of information transfers. As for data integrity, Class 3 Flow control has this handled by higher-level protocols such as TCP due to Fibre Channel not checking the corrupted or missing frames. Hence any discovery of a corrupted packet by the higher-level protocol on the receiving device instantly initiates a retransmission of the sequence. All of this sounds great until the non-acknowledgement of rejected frames starts to also bring about Class 3's disadvantage. This is that inevitably a Fabric will become busy with traffic and will consequently discard frames, hence the name Class 3 discards. Due to this the receiving device's higher-level protocol's subsequent request for retransmission of sequences will then degrade the device and fabric throughput.

Another indication of Class 3 discards are zoning conflicts where a frame has been transmitted and cannot reach a destination, hence concluding in the SAN initiating a Class 3 discard. This is caused by either legacy or zoning mistakes where for example a decommissioned Storage system was not unzoned from a server or vice versa leading to continuous frames being discarded and degraded throughput as sequences are retransmitted. This then results in performance problems, potential application degradation and automatic finger pointing at the Storage System for a problem that can't automatically be identified. By resolving the zoning conflict and spreading the load of the SAN throughput across the right ports, the heavy traffic or zoning issues which cause the Class 3 discards can be quickly removed bringing immediate performance and throughput improvements. By gaining an insight into the occurrence and amount of Class 3 discards, huge performance problems can be quickly remediated before they occur and thus another reason as to why the Storage shouldn't automatically be blamed.

These are just some of the metrics / signs to look for which can ultimately save you from weeks of troubleshooting and guessing. By first acknowledging these metrics, identifying when they occur and proactively eliminating them, the SAN storage environment will quickly evolve and transform into a healthy, proactive and optimized one. Furthermore by eliminating each of these issues you also empower yourself by eliminating their consequent problems such as application slowdown, poor response times, unplanned outages and long drawn out troubleshooting exercises which eventually lead to fingerpointing fights. Ideally what will occur is a paradigm shift where instead of application owners complaining to the Storage team, the Storage team will proactively identify problems prior to their existence. Here lies the key to making the ‘always blaming the Storage' syndrome a thing of the past.

More Stories By Archie Hendryx

SAN, NAS, Back Up / Recovery & Virtualisation Specialist.

@ThingsExpo Stories
DX World EXPO, LLC, a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Conference Guru has been named “Media Sponsor” of the 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. A valuable conference experience generates new contacts, sales leads, potential strategic partners and potential investors; helps gather competitive intelligence and even provides inspiration for new products and services. Conference Guru works with conference organizers to pass great deals to gre...
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develop...
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...
"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.
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
Large industrial manufacturing organizations are adopting the agile principles of cloud software companies. The industrial manufacturing development process has not scaled over time. Now that design CAD teams are geographically distributed, centralizing their work is key. With large multi-gigabyte projects, outdated tools have stifled industrial team agility, time-to-market milestones, and impacted P&L stakeholders.
"Akvelon is a software development company and we also provide consultancy services to folks who are looking to scale or accelerate their engineering roadmaps," explained Jeremiah Mothersell, Marketing Manager at Akvelon, 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.
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, 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.
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, 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.
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.