Click here to close now.

Welcome!

Cloud Expo Authors: Carmen Gonzalez, Elizabeth White, Ian Khan, Liz McMillan, William Schmarzo

Related Topics: Virtualization, Java, Microservices Journal, Open Source, Cloud Expo

Virtualization: Article

Considerations for SSD Deployments

SSD is a great technology, but your best value from it will come when you deploy it most efficiently

Legacy storage architectures do not perform very efficiently in virtual computing environments. The very random, very write-intensive I/O patterns generated by virtual hosts drive storage costs up as enterprises either add spindles or look to newer storage technologies like solid state disk (SSD) to address the IOPS shortfall.

SSD costs are coming down, but they are still significantly higher than spinning disk costs. When enterprises do consider SSD, how it is used and where it is placed in the virtual infrastructure can make a big difference in how much enterprises have to spend to meet their performance requirements. It can also impose certain operational limitations that may or may not be issues in specific environments.

Some of the key considerations that need to be taken into account are SSD placement (in the host or in the SAN), high availability/failover requirements, caching vs logging architectures, and the value of preserving existing investments vs rip and replace investments that promise storage hardware specifically designed for virtual environments.

SSD Placement
There are two basic locations to place SSD, each of which offers its own pros and cons. Host-based SSD will generally offer the lowest storage latencies, particularly if the SSD is located on PCIe cards. In non-clustered environments where it is clear that IOPS and storage latencies are the key performance problems, these types of devices can be very valuable. In most cases, they will remove storage as the performance problem.

But don't necessarily expect that in your environment, these devices will deliver their rated IOPS directly to your applications. In removing storage as the bottleneck, system performance will now be determined by whatever the next bottleneck in the system is. That could be CPU, memory, operating system, or any number of other potential issues. This phenomenon is referred to as Amdahl's Law.

What you probably care about are application IOPS. Test the devices you're considering in your environment before purchase, so you know exactly the level of performance gain they will provide to you. Then you can make a more informed decision about whether or not you can cost justify them for use with your workloads. Paying for performance you can't use is like buying a Ferrari for use on America's interstate system - you may never get out of second gear.

Raw SSD technology generally can provide blazingly fast read performance. Write performance, however, varies depending on whether you are writing randomly or sequentially. The raw technical specs on many SSD devices indicate that sequential write performance may be half that of read performance, and random write performance may be half again as slow. Write latencies may also not be deterministic because of how SSD devices manage the space they are writing to. Many SSD vendors are combining software and other infrastructure around their SSD devices to address some of these issues. If you're looking at SSD, look to the software it's packaged with to make sure the SSD capacity you're buying can be used most efficiently.

Host-based SSD introduces failover limitations. If you have implemented a product like VMware HA in your environment to automatically recover failed nodes, any data sitting in a host-based SSD device that has not been written through to shared storage will not be available on recovery. This can lead to data loss on recovery - something that may or may not be an issue in your environment. Even though SSD is non-volatile storage, if the node it is sitting in is down, you can't get to it. You can get to it after that node is recovered, but the issue here is whether or not you can automatically fail over and have access to it.

Because of this issue, most host-based SSD products implement what is called a "write-through" cache, which means that they don't acknowledge writes at SSD latencies, they actually write them through to shared disk and then send the write acknowledgement back from there. Anything on shared disk can be potentially recovered by any other node in the cluster, ensuring that no committed data is unavailable on failover. But what this means is that you won't get any write performance improvements from SSD, just better read performance.

What does your workload look like in terms of read vs write percentages? Most virtual environments are very write intensive, much more so than they ever were in physical environments, and virtual desktop infrastructure (VDI) environments can be as much as 90% writes when operating in steady state mode. If write performance is your problem, host-based SSD with a write-through cache may not help very much in the big picture.

SAN-based SSD, on the other hand, can support failover without data loss, and if implemented with a write-back cache can provide write performance speedups as well. But many implementations available for use with SAN arrays are really only designed to speed up reads. Check carefully as you consider SSD to understand how it is implemented, and how well that maps to the actual performance requirements in your environment.

Caching vs Logging Architectures
Most SSD, wherever it is implemented, is used as a cache. Sizing guidelines for caches start with the cache as a percentage of the back-end storage it is front-ending. Generally the cache needs to be somewhere between 3% to 6% of the back-end storage, so larger data store capacities require larger caches. For example, 20TB of back-end data might require 1TB of SSD cache (5%).

Caches are generally just speeding up reads, but if you are working with a write-back cache, then the cache will have to be split between SSD capacity used to speed up reads and SSD capacity used to speed up writes. Everything else being equal in terms of performance requirements, write-back caches will have to be larger than write-through caches, but will provide more balanced performance gains (across both reads and writes).

Logging architectures, by definition, speed up writes, making them a good fit for write-intensive workloads like those found in virtual computing environments. Logs provide write performance gains by taking the very random workload and essentially removing the randomness from it by writing it sequentially to a log, acknowledging the writes from there, then asynchronously de-staging them to a shared storage pool. This means that the same SSD device used in a log vs used in a cache will be faster, assuming some randomness to the workload. The write performance the guest VMs see is the performance of the log device operating in sequential write mode almost all the time, and it can result in write performance improvements of up to 10x (relative to that same device operating in the random mode it would normally be operating in). And a log provides write performance improvements for all writes from all VMs all the time. (What's also interesting is that if you are getting 10x the IOPS from your current spinning disk, given Amdahl's Law, you may not even need to purchase SSD to remove storage as the performance bottleneck.)

Logs are very small (10GB or so) and are dedicated to a host, while the shared storage pool is accessible to all nodes in a cluster and primarily handles read requests. In a 20 node cluster with 20TB of shared data, you would need 200GB for the logs (10GB x 20 hosts) vs the 1TB you would need if SSD was used as a cache. Logs are much more efficient than caches for write performance improvements, resulting in lower costs.

If logs are located on SAN-based SSD, you not only get the write performance improvements, but this design fully supports node failover without data loss, a very nice differentiator from write-through cache implementations.

But what about read performance? This is where caches excel, and a write log doesn't seem to address that. That's true, and why it's important to combine a logging architecture with storage tiering. Any SSD capacity not used by the logs can be configured into a fast tier 0, which will provide the read performance improvements for any data residing in that tier. The bottom line here is that you can get better overall storage performance improvements from a "log + tiering" design than you can from a cache design while using 50% - 90% less high performance device (in this case, SSD) capacity. In our example above, if you buy a 256GB SAN-based SSD device and use it in a 20 node cluster, you'll get SSD sequential write performance for every write all the time, and have 56GB left over to put into a tier 0. Compare that to buying 1TB+ of cache capacity at SSD prices.

With single image management technology like linked clones or other similar implementations, you can lock your VM templates into this tier, and very efficiently gain read performance improvements against the shared blocks in those templates for all child VMs all the time. Single image management technology can help make the use of SSD capacity more efficient in either a cache or a log architecture, so don't overlook it as long as it is implemented in a way that does not impinge upon your storage performance.

Purpose-Built Storage Hardware
There are some interesting new array designs that leverage SSD, sometimes in combination with some of the other technologies mentioned above (log architectures, storage tiering, single image manage-ment, spinning disk). Designed specifically with the storage performance issues in virtual environments in mind, there is no doubt that these arrays can outperform legacy arrays. But for most enterprises, that may not be the operative question.

It's rare that an enterprise doesn't already have a sizable investment in storage. Many of these existing arrays support SSD, which can be deployed in a SAN-based cache or fast tier. It's much easier, and potentially much less disruptive and expensive if existing storage investments could be leveraged to address the storage performance issues in virtual environments. It's also less risky, since most of the hot new "virtual computing-aware" arrays and appliances are built by startups, not proven vendors. If there are pure software-based options to consider that support heterogeneous storage hardware and can address the storage issues common in virtual computing environments, allowing you to potentially take advantage of SSD capacity that fits into your current arrays, this could be a simpler, more cost-effective, and less risky option than buying from a storage startup. But only, of course, if it adequately resolves your performance problem.

The Take-Away
If there's one point you should take away from this article, it's that just blindly throwing SSD at a storage performance problem in virtual computing environments is not going to be a very efficient or cost-effective way to address your particular issues. Consider how much more performance you need, whether you need it on reads, writes, or both, whether you need to failover without data loss, and whether preserving existing storage hardware investments is important to you. SSD is a great technology, but your best value from it will come when you deploy it most efficiently.

More Stories By Eric Burgener

Eric Burgener is vice president product management at Virsto Software. He has worked on emerging technologies for almost his entire career, with early stints at pioneering companies such as Tandem, Pyramid, Sun, Veritas, ConvergeNet, Mendocino, and Topio, among others, on fault tolerance and high availability, replication, backup, continuous data protection, and server virtualization technologies.

Over the last 25 years Eric has worked across a variety of functional areas, including sales, product management, marketing, business development, and technical support, and also spent time as an Executive in Residence with Mayfield and a storage industry analyst at Taneja Group. Before joining Virsto, he was VP of Marketing at InMage.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@CloudExpo Stories
All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades. With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo, June 9-11, 2015, at the Javits Center in New York City. Learn what is going on, contribute to the discussions, and ensure that your enter...
The security devil is always in the details of the attack: the ones you've endured, the ones you prepare yourself to fend off, and the ones that, you fear, will catch you completely unaware and defenseless. The Internet of Things (IoT) is nothing if not an endless proliferation of details. It's the vision of a world in which continuous Internet connectivity and addressability is embedded into a growing range of human artifacts, into the natural world, and even into our smartphones, appliances, a...
In a recent research, analyst firm IDC found that the average cost of a critical application failure is $500,000 to $1 million per hour and the average total cost of unplanned application downtime is $1.25 billion to $2.5 billion per year for Fortune 1000 companies. In addition to the findings on the cost of the downtime, the research also highlighted best practices for development, testing, application support, infrastructure, and operations teams.
There is no doubt that Big Data is here and getting bigger every day. Building a Big Data infrastructure today is no easy task. There are an enormous number of choices for database engines and technologies. To make things even more challenging, requirements are getting more sophisticated, and the standard paradigm of supporting historical analytics queries is often just one facet of what is needed. As Big Data growth continues, organizations are demanding real-time access to data, allowing immed...
T-Mobile has been transforming the wireless industry with its “Uncarrier” initiatives. Today as T-Mobile’s IT organization works to transform itself in a like manner, technical foundations built over the last couple of years are now key to their drive for more Agile delivery practices. In his session at DevOps Summit, Martin Krienke, Sr Development Manager at T-Mobile, will discuss where they started their Continuous Delivery journey, where they are today, and where they are going in an effort ...
Enterprises are fast realizing the importance of integrating SaaS/Cloud applications, API and on-premises data and processes, to unleash hidden value. This webinar explores how managers can use a Microservice-centric approach to aggressively tackle the unexpected new integration challenges posed by proliferation of cloud, mobile, social and big data projects. Industry analyst and SOA expert Jason Bloomberg will strip away the hype from microservices, and clearly identify their advantages and d...
Container frameworks, such as Docker, provide a variety of benefits, including density of deployment across infrastructure, convenience for application developers to push updates with low operational hand-holding, and a fairly well-defined deployment workflow that can be orchestrated. Container frameworks also enable a DevOps approach to application development by cleanly separating concerns between operations and development teams. But running multi-container, multi-server apps with containers ...
Software Development Solution category in The 2015 American Business Awards, and will ultimately be a Gold, Silver, or Bronze Stevie® Award winner in the program. More than 3,300 nominations from organizations of all sizes and in virtually every industry were submitted this year for consideration. "We are honored to be recognized as a leader in the software development industry by the Stevie Awards judges," said Steve Brodie, CEO of Electric Cloud. "We introduced ElectricFlow and our Deploy app...
What do a firewall and a fortress have in common? They are no longer strong enough to protect the valuables housed inside. Like the walls of an old fortress, the cracks in the firewall are allowing the bad guys to slip in - unannounced and unnoticed. By the time these thieves get in, the damage is already done and the network is already compromised. Intellectual property is easily slipped out the back door leaving no trace of forced entry. If we want to reign in on these cybercriminals, it's hig...
SYS-CON Events announced today that DragonGlass, an enterprise search platform, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. After eleven years of designing and building custom applications, OpenCrowd has launched DragonGlass, a cloud-based platform that enables the development of search-based applications. These are a new breed of applications that utilize a search index as their backbone for data...
Mobile commerce traffic is surpassing desktop, yet less than 20% of sales in the U.S. are mobile commerce sales. In his session at 15th Cloud Expo, Dan Franklin, Segment Manager, Commerce, at Verizon Digital Media Services, defined mobile devices and discussed how next generation means simplification. It means taking your digital content and turning it into instantly gratifying experiences.
SYS-CON Events announced today that EnterpriseDB (EDB), the leading worldwide provider of enterprise-class Postgres products and database compatibility solutions, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. EDB is the largest provider of Postgres software and services that provides enterprise-class performance and scalability and the open source freedom to divert budget from more costly traditiona...
Fundamentally, SDN is still mostly about network plumbing. While plumbing may be useful to tinker with, what you can do with your plumbing is far more intriguing. A rigid interpretation of SDN confines it to Layers 2 and 3, and that's reasonable. But SDN opens opportunities for novel constructions in Layers 4 to 7 that solve real operational problems in data centers. "Data center," in fact, might become anachronistic - data is everywhere, constantly on the move, seemingly always overflowing. Net...
Gartner predicts that the bulk of new IT spending by 2016 will be for cloud platforms and applications and that nearly half of large enterprises will have cloud deployments by the end of 2017. The benefits of the cloud may be clear for applications that can tolerate brief periods of downtime, but for critical applications like SQL Server, Oracle and SAP, companies need a strategy for HA and DR protection. While traditional SAN-based clusters are not possible in these environments, SANless cluste...
Software Defined Storage provides many benefits for customers including agility, flexibility, faster adoption of new technology and cost effectiveness. However, for IT organizations it can be challenging and complex to build your Enterprise Grade Storage from software. In his session at Cloud Expo, Paul Turner, CMO at Cloudian, looked at the new Original Design Manufacturer (ODM) market and how it is changing the storage world. Now Software Defined Storage companies can build Enterprise grade ...
Discussions about cloud computing are evolving into discussions about enterprise IT in general. As enterprises increasingly migrate toward their own unique clouds, new issues such as the use of containers and microservices emerge to keep things interesting. In this Power Panel at 16th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists will address the state of cloud computing today, and what enterprise IT professionals need to know about how the latest topics and trends affec...
There's Big Data, then there's really Big Data from the Internet of Things. IoT is evolving to include many data possibilities like new types of event, log and network data. The volumes are enormous, generating tens of billions of logs per day, which raise data challenges. Early IoT deployments are relying heavily on both the cloud and managed service providers to navigate these challenges. In her session at Big Data Expo®, Hannah Smalltree, Director at Treasure Data, discussed how IoT, Big D...
Buzzword alert: Microservices and IoT at a DevOps conference? What could possibly go wrong? In this Power Panel at DevOps Summit, moderated by Jason Bloomberg, the leading expert on architecting agility for the enterprise and president of Intellyx, panelists will peel away the buzz and discuss the important architectural principles behind implementing IoT solutions for the enterprise. As remote IoT devices and sensors become increasingly intelligent, they become part of our distributed cloud en...
To manage complex web services with lots of calls to the cloud, many businesses have invested in Application Performance Management (APM) and Network Performance Management (NPM) tools. Together APM and NPM tools are essential aids in improving a business's infrastructure required to support an effective web experience... but they are missing a critical component - Internet visibility. Internet connectivity has always played a role in customer access to web presence, but in the past few years u...
SYS-CON Events announced today that MetraTech, now part of Ericsson, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Ericsson is the driving force behind the Networked Society- a world leader in communications infrastructure, software and services. Some 40% of the world’s mobile traffic runs through networks Ericsson has supplied, serving more than 2.5 billion subscribers.