Condusiv Technologies Blog

Condusiv Technologies Blog

Blogging @Condusiv

The Condusiv blog shares insight into the issues surrounding system and application performance—and how I/O optimization software is breaking new ground in solving those issues.

Solving the IO Blender Effect with Software-Based Caching

by Spencer Allingham 5. July 2018 07:30

First, let me explain exactly what the IO Blender Effect is, and why it causes a problem in virtualized environments such as those from VMware or Microsoft’s Hyper-V.



This is typically what storage IO traffic would look like when everything is working well. You have the least number of storage IO packets, each carrying a large payload of data down to the storage. Because the data is arriving in large chunks at a time, the storage controller has the opportunity to create large stripes across its media, using the least number of storage-level operations before being able to acknowledge that the write has been successful.



Unfortunately, all too often the Windows Write Driver is forced to split data that it’s writing into many more, much smaller IO packets. These split IO situations cause data to be transferred far less efficiently, and this adds overhead to each write and subsequent read. Now that the storage controller is only receiving data in much smaller chunks at a time, it can only create much smaller stripes across its media, meaning many more storage operations are required to process each gigabyte of storage IO traffic.


This is not only true when writing data, but also if you need to read that data back at some later time.

But what does this really mean in real-world terms?

It means that an average gigabyte of storage IO traffic that should take perhaps 2,000 or 3,000 storage IO packets to complete, is now taking 30,000, or 40,000 storage IO packets instead. The data transfer has been split into many more, much smaller, fractured IO packets. Each storage IO operation that has to be generated takes a measurable amount of time and system resource to process, and so this is bad for performance! It will cause your workloads to run slower than they should, and this will worsen over time unless you perform some time and resource-costly maintenance.

So, what about the IO Blender Effect?

Well, the IO Blender Effect can amplify the performance penalty (or Windows IO Performance Tax) in a virtualized environment. Here’s how it works…

 

As the small, fractured IO traffic from several virtual machines passes through the physical host hypervisor (Hyper-V server or VMware ESX server), the hypervisor acts like a blender. It mixes these IO streams, which causes a randomization of the storage IO packets, before sending out what is now a chaotic mess of small, fractured and now very random IO streams out to the storage controller.

It doesn’t matter what type of storage you have on the back-end. It could be direct attached disks in the physical host machine, or a Storage Area Network (SAN), this type of storage IO profile couldn’t be less storage-friendly.

The storage is now only receiving data in small chunks at a time, and won’t understand the relationship between the packets, so it now only has the opportunity to create very small stripes across its media, and that unfortunately means many more storage operations are required before it can send an acknowledgement of the data transfer back up to the Windows operating system that originated it.

How can RAM caching alleviate the problem?

 

Firstly, to be truly effective the RAM caching needs to be done at the Windows operating system layer. This provides the shortest IO path for read IO requests that can be satisfied from server-side RAM, provisioned to each virtual machine. By satisfying as many “Hot Reads” from RAM as possible, you now have a situation where not only are those read requests being satisfied faster, but those requests are now not having to go out to storage. That means less storage IO packets for the hypervisor to blend.

Furthermore, the V-locity® caching software from Condusiv Technologies also employs a patented technology called IntelliWrite®. This intelligently helps the Windows Write Driver make better choices when writing data out to disk, which avoids many of the split IO situations that would then be made worse by the IO Blender Effect. You now get back to that ideal situation of healthy IO; large, sequential writes and reads.

Is RAM caching a disruptive solution?

 

No! Not at all, if done properly.

Condusiv’s V-locity software for virtualised environments is completely non-disruptive to live, running workloads such as SQL Servers, Microsoft Dynamics, Business Information (BI) solutions such as IBM Cognos, or other important workloads such as SAP, Oracle and the such.

In fact, all you need to do to test this for yourself is download a free trialware copy from:

www.condusiv.com/try

Just install it! There are no reboots required, and it will start working in just a couple of minutes. If you decide that it isn’t for you, then uninstall it just as easily. No reboots, no disruption!


How to Improve Application Performance by Decreasing Disk Latency like an IT Engineer

by Spencer Allingham 13. June 2018 06:49

You might be responsible for a busy SQL server, for example, or a Web Server; perhaps a busy file and print server, the Finance Department's systems, documentation management, CRM, BI, or something else entirely.

Now, think about WHY these are the workloads that you care about the most?

 

Were YOU responsible for installing the application running the workload for your company? Is the workload being run business critical, or considered TOO BIG TO FAIL?

Or is it simply because users, or even worse, customers, complain about performance?

 

If the last question made you wince, because you know that YOU are responsible for some of the workloads running in your organisation that would benefit from additional performance, please read on. This article is just for you, even if you don't consider yourself a "Techie".

Before we get started, you should know that there are many variables that can affect the performance of the applications that you care about the most. The slowest, most restrictive of these is referred to as the "Bottleneck". Think of water being poured from a bottle. The water can only flow as fast as the neck of the bottle, the 'slowest' part of the bottle.

Don't worry though, in a computer the bottleneck will pretty much always fit into one of the following categories:

•           CPU

•           DISK

•           MEMORY

•           NETWORK

The good news is that if you're running Windows, it is usually very easy to find out which one the bottleneck is in, and here is how to do it (like an IT Engineer):

 •          Open Resource Monitor by clicking the Start menu, typing "resource monitor", and pressing Enter. Microsoft includes this as part of the Windows operating system and it is already installed.

 •          Do you see the graphs in the right-hand pane? When your computer is running at peak load, or users are complaining about performance, which of the graphs are 'maxing out'?

This is a great indicator of where your workload's bottleneck is to be found.         

 

SO, now you have identified the slowest part of your 'compute environment' (continue reading for more details), what can you do to improve it?

The traditional approach to solving computer performance issues has been to throw hardware at the solution. This could be treating yourself to a new laptop, or putting more RAM into your workstation, or on the more extreme end, buying new servers or expensive storage solutions.

BUT, how do you know when it is appropriate to spend money on new or additional hardware, and when it isn't. Well the answer is; 'when you can get the performance that you need', with the existing hardware infrastructure that you have already bought and paid for. You wouldn't replace your car, just because it needed a service, would you?

Let's take disk speed as an example.  Let’s take a look at the response time column in Resource Monitor. Make sure you open the monitor to full screen or large enough to see the data.  Then open the Disk Activity section so you can see the Response Time column.  Do it now on the computer you're using to read this. (You didn't close Resource Monitor yet, did you?) This is showing the Disk Response Time, or put another way, how long is the storage taking to read and write data? Of course, slower disk speed = slower performance, but what is considered good disk speed and bad?

To answer that question, I will refer to a great blog post by Scott Lowe, that you can read here...

https://www.techrepublic.com/blog/the-enterprise-cloud/use-resource-monitor-to-monitor-storage-performance/

In it, the author perfectly describes what to expect from faster and slower Disk Response Times:

"Response Time (ms). Disk response time in milliseconds. For this metric, a lower number is definitely better; in general, anything less than 10 ms is considered good performance. If you occasionally go beyond 10 ms, you should be okay, but if the system is consistently waiting more than 20 ms for response from the storage, then you may have a problem that needs attention, and it's likely that users will notice performance degradation. At 50 ms and greater, the problem is serious."

Hopefully when you checked on your computer, the Disk Response Time is below 20 milliseconds. BUT, what about those other workloads that you were thinking about earlier. What's the Disk Response Times on that busy SQL server, the CRM or BI platform, or those Windows servers that the users complain about?

If the Disk Response Times are often higher than 20 milliseconds, and you need to improve the performance, then it's choice time and there are basically two options:

           In my opinion as an IT Engineer, the most sensible option is to use storage workload reduction software like Diskeeper for physical Windows computers, or V-locity for virtualised Windows computers. These will reduce Disk Storage Times by allowing a good percentage of the data that your applications need to read, to come from a RAM cache, rather than slower disk storage. This works because RAM is much faster than the media in your disk storage. Best of all, the only thing you need to do to try it, is download a free copy of the 30 day trial. You don't even have to reboot the computer; just check and see if it is able to bring the Disk Response Times down for the workloads that you care about the most.

           If you have tried the Diskeeper or V-locity software, and you STILL need faster disk access, then, I'm afraid, it's time to start getting quotations for new hardware. It does make sense though, to take a couple of minutes to install Diskeeper or V-locity first, to see if this step can be avoided. The software solution to remove storage inefficiencies is typically a much more cost-effective solution than having to buy hardware!

Visit www.condusiv.com/try to download Diskeeper and V-locity now, for your free trial.

 

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