VMdamentals

It is certainly not unheared of – “When I delete a snapshot from a VM, the thing totally freezes!“. The strange thing is, some customers have these issues, others don’t (or are not aware of it). So what really DOES happen when you clean out a snapshot? Time to investigate!

Test Setup

So how do we test performance impact on storage while ruling out external factors? The setup I choose was using a VM with the following specs:

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In part one I covered all stuff you can think of in regards to delays and latencies you encounter on physical disk drives and solid states. Now it is time to see how we can string together multiple drives in order to get the performance and storage space we actually require. I’ll discuss RAID types, number of disks in such a RAID set, segment sizes to optimize your storage for particular needs and so on.

–> For those of you who haven’t read part 1 yet: Thoughput Part1: The Basics

A short intro to RAID types

Now finally it is on to the stringing together of disks. More disks is more space, more performance, right? Yes right – sometimes. I am not zooming in too deep on the RAID types. I assume you have some knowledge on different types of RAID, mainly RAID1, RAID10 and RAID5. All that I’ll say about it: Read the rest of this entry »

As I tackle more and more disk performance related issues, I thought it was time to create a series of blogposts about spindles, seektimes, latency and all that stuff. For now part 1, which covers the basics. Things like raid type, rotational speeds and seektimes basically make up “how fast you will go”. On to the dirty details!

Introduction to physical disks and their behaviour

So what is really important when looking at physical disks, and their performance? Firstly and most important, we must look at the storage system parameters in order to reduce disk latencies. In order to be able to do this properly, we have to take into account the characteristics of the I/O what is being performed. Secondly, we have to look at segment sizes within the chosen raid types (which in turn followes from the system parameters). Finally, we’ll deepdive into alignment (which still appears to be misunderstood by a lot of people)
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A hugely underestimated requirement in larger VDI environments is disk IOPs. A lot of the larger VDI implementations have failed using SATA spindles, when you use 15K SAS or FC disks you get away with it most of the times (as long as you do not scale up too much). I have been looking at ways to get more done using less (especially in current times, who doesn’t!). Dataman, the dutch company I work for (www.dataman.nl) teamed up with Sun Netherlands and their testing facility in Linlithgow, Scotland for testing. I got the honours of performing the tests, and I almost literally broke the sound barrier using Suns newest line of Unified Storage: The 7000 series. Why can you break the sound barrier with this type of storage? Watch the story unroll! For now part one… The intro.

What VMware View offers… And needs

Before a performance test even came to mind, I started to figure what VMware View offers, and what it needs. It is obvious: View gives you linked cloning technology. This means, that only a few full clones (called replicas) are read by a lot of Virtual Desktops (or vDesktops as I will call them from now on) in parallel. So what would really help pushing the limits of your storage? Exactly, a very large cache or solid-state disks. Read the rest of this entry »

No rocket science here. esxtop has always been there. Yet a lot of people miss out on some of its great features. Hopefully this blogpost will get you interested in looking at esxtop (again?) in detail!

Yesterday I attended a very interesting breakout session about esxtop and its advanced features in vSphere. Old news you might say, but there is SO much you can do with esxtop. For example, you can export data from esxtop and import them in Windows perfmon. And if you did know that, then for example, did you know you can now actually see which physic NIC is being used by a certain VM?

Other neat little features were shown. The best one being that the “swcur” field is actually NOT about the current swapping activity of a VM, but swapping that occured in the past (yes, I too would have called it differently…). How many of you knew that one? Finally, a very interesting field in the storage screen (yes for those who did not know that one, esxtop is not just about CPU, but also memory, storage, and new in vSphere… Interrupts) ). This field is called “DAVG” and this shows the actual latency seen by ESX to your storage (and also KAVG for kernel latency and GAVG for the total latency the guest sees).

There were also a few examples of misbehaving VMs which was very interesting to see. Numbers which seemed not possible, yet explained perfectly. I would like to vote this very last presentation at VMworld 2009 the best technical presentation I witnessed there!

I hope I got you (re)interested in esxtop. I am more of a graphical guy, so I like the performance monitor embedded within the VI client. But some things just aren’t there. So esxtop is definitely worth a(nother) look. If you’re using ESXi, make sure to download the vMA appliance (here) which has resxtop included (which looks a lot like esxtop on ESX).