Tag Archives: ESX

SQL & Exchange performance in a Virtual Machine

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The below is something I see far to often: An SQL or Exchange virtual machine using a single LSI Logic SAS virtual SCSI controller.

LSIlogic

What is even worse is a virtual machine using a single LSI controller and a single virtual disk for one or more databases and logs (as shown above).

Why is this so common?

Probably because the LSI Logic SAS controller is the default for Windows 2008/2012 virtual machines and additional SCSI controllers are not automatically added until you have more than 16 virtual disks for a single VM.

Why is this a problem?

The LSI controller has a queue depth limit of 128, compared to the default limit for PVSCSI which is 256, however it can be tuned to 1024 for higher performance requirements.

As a result, the a configuration with a single LSI controller and/or a limited number of virtual disks can artificially significantly constrain the underlying storage from delivering the performance it is capable of.

Another problem with the LSI controller is the amount of CPU it uses is higher than the PVSCSI controller for the same IO levels. This means you’re wasting virtual machine (and the underlying hosts) CPU resources unnecessarily.

Using more CPU could lead to other problems such as CPU Ready which can also lead to reduced performance.

A colleague and friend of mine, Michael Webster wrote a great post titled: Performance Issues Due To Virtual SCSI Device Queue Depths where he shows the performance difference between SATA, LSI and PVSCSI controllers. I highly recommend having a read of this post.

What is the solution?

Using multiple Paravirtual (PVSCSI) adapters with virtual disks evenly spread over the four controllers for Windows virtual machines is a no brainer!

This results in:

  1. Higher default queue depth
  2. Lower CPU overheads
  3. Higher potential performance

How do I configure this?

It’s fairly straight forward, but don’t just change the LSI Controller too PVSCSI as the Guest OS may not have the driver installed which will result in the VM failing to boot.

Too avoid this, simply edit the virtual machine and add a new Virtual Disk of any size and for the virtual device node, select SCSI (1:0) and follow the prompts.

VirtualDiskSCSI10

Once the new virtual disk is added you should see a new LSI Logic SAS SCSI controller is added as shown below.

NewLSIController

Next highlight the adapter and select “Change Type” in the top right hand corner of the window and select Paravirtual. Once this is complete you should see similar to the below:

AddPVSCSIController

Next hit “Ok” and the new Controller and virtual disk will be added to the VM.

Now we open the console of the VM and open Compute Management and goto Device Manager. Under Storage Controllers you should now see VMware PVSCSI Controller as shown below.

DeviceManagerPVSCSI

Now we are safe to Shutdown the VM.

Once the VM is shutdown, Edit the VM setting and highlight the SCSI Controller 0 and select Change Type as we did earlier and select Paravirtual. Once this is done you will see the original controller is replaced with a new controller.

ChangeLSItoPVSCSI

Now that we have the boot drive change to PVSCSI, we can now balance the data drives across up to four PVSCSI controllers for maximum performance.

To do this, simply highlight a Virtual Disk and drop down the Virtual Device Node and select SCSI (1:0) or any other available slot on the SCSI (1:x) controller.

ChangeControllerID

After doing this you will see new SCSI controllers appear and you need to change these to Paravirtual as we have done to the first controller.

ChangeControllerIDMultipleVdisks

For each of the virtual disks, ensure they are placed evenly across the PVSCSI controllers. For example, if you have a VM with eight virtual disks plus the OS disk, it should look like this:

Virtual Disk 1 (OS) : SCSI (0:0)
Virtual Disk 2 (OS) : SCSI (0:1)
Virtual Disk 3 (OS) : SCSI (1:0)
Virtual Disk 4 (OS) : SCSI (1:1)
Virtual Disk 5 (OS) : SCSI (2:0)
Virtual Disk 6 (OS) : SCSI (2:1)
Virtual Disk 7 (OS) : SCSI (3:0)
Virtual Disk 8 (OS) : SCSI (3:1)
Virtual Disk 9 (OS) : SCSI (0:2)

This results in two data virtual disks per PVSCSI controller which evenly distributes IO across all controllers with the exception being first controller (SCSI 0) also hosting the OS drive.

What if I have problems?

On occasions I have seen problems with this process which has resulted in VMs not booting, however these issues are easy to fix.

If your VM fails to boot with a message like “Operating System not found”, I suggest you panic! Just kidding, this is typically just the boot order of the Virtual machine has been screwed up. Just go into the bios and check the boot order has the PVSCSI controller showing and the correct virtual disk in first priority.

If the VM boots and BSOD or crashes and goes into a continuous reboot loop then power off the VM and set the first SCSI controller where the boot disk is running back to LSI. Then reboot the VM and make sure the PVSCSI driver is showing up (if its not you didn’t follow the above instructions) so go back and follow them so the PVSCSI driver is loaded and working, then shutdown and change the SCSI controller back to PVSCSI and you should be fine.

If the VM boots and one or more drives do not show up in my computer, go into Disk Manager and you may see the drives are marked as offline. Simply right click the drive and mark it as online and reboot and you’re good to go.

Summary:

If you have made the intelligent move to virtualize your business critical applications, firstly congratulations! However as with physical hardware, Virtual machines also have optimal configurations so make sure you use PVSCSI controllers with multiple virtual disks and have your DBA span the database across multiple virtual disks for maximum performance.

The following post shows how to do this in detail:

Splitting SQL datafiles across multiple VMDKs for optimal VM performance

If the DBA is not confident doing this, you can also just add multiple virtual disks (connected via multiple PVSCSI controllers) and create a stripe in guest (via Disk Manager) and this will also give you the benefit of multiple vdisks.

Related Articles:

1. Peak Performance vs Real World Performance

2. Enterprise Architecture & Avoiding tunnel vision

3. Microsoft Exchange 2013/2016 Jetstress Performance Testing on Nutanix Acropolis Hypervisor (AHV)

In-Kernel verses Virtual Storage Appliance

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Let me start by asking, What’s all this “In-Kernel verses Virtual Storage Appliance” debate all about?

It seems to me to be total nonsense yet it is the focus of so called competitive intelligence and twitter debates. From an architectural perspective I just don’t get why it’s such a huge focus when there are so many other critical areas to focus on, like the benefit of Hyper-Converged vs SAN/NAS!!!

Saying In-Kernel or VSA is faster than the other (just because of where the software runs) is like saying my car with 18″ wheels is faster than your car with 17″ wheels. In reality there are so many other factors to consider, the wheel size is almost irrelevant, as is whether or not storage is provided “In-Kernel” or via a “Virtual Appliance”.

If something is In-Kernel, it doesn’t mean it’s efficient, it could be In-Kernel and really inefficient code, therefore being much worse than a VSA solution, or a VSA could be really inefficient and an In-Kernel solution could be more efficient.

In addition to this, Hyper-converged solutions are by design scale-out solutions, as a result the performance capabilities are the sum of all the nodes, not one individual node.

As long as a solution can provide enough performance (IOPS) per node for individual (or scaled up) VMs and enough scale-out to support all the customers VMs, it doesn’t matter if Solution A is In-Kernel or VSA, or that the solution can do 20% or even 100% more IOPS per node compared to solution B. The only thing that matters is the customers requirements are met/exceeded.

Let’s shift focus for a moment and talk about the performance capabilities of the ESX/ESXi hypervisor as this seems to be argued as an significant overhead which prevents a VSA from being high performance. In my experience , ESXi has never been a significant I/O bottleneck, even for large customers with business critical applications as the focus on Biz Critical Apps really took off around the VI3 days or later where the hypervisor could deliver ~100K IOPS per host.

The below is a chart showing VMware’s tested capabilities from ESX 1, through to vSphere 5 which was released in July 2011.

IOPSvmware

What we can clearly see is vSphere 5.0 can achieve 1 Million IOPS (per host), and even back in the VI3 days, 100,000 IOPS.

In 2011, VMware wrote a great article “Achieving a Million I/O Operations per Second from a Single VMware vSphere® 5.0 Host” which shows how the 1 million IOPS claim has been validated.

In 2012 VMware published “1 million IOPS On 1VM” which showed not only could vSphere achieve a million IOPS, but it could do it from 1 VM.

I don’t know about you, but it’s pretty impressive VMware has optimized the hypervisor to the point where a single VM can get 1 million IOPS, and that was back in 2012!

Now in both the articles, the 1 million IOPS was achieved using a traditional centralised SAN, the first article was with an EMC VMAX with 8 engines and I have summarized the setup below.

  • 4 quad-core processors and 128GB of memory per engine
  • 64 front-end 8Gbps Fibre Channel (FC) ports
  • 64 back-end 4Gbps FC ports
  • 960 * 15K RPM, 450GB FC drives

The IO profile for this test was 8K , 100% read, 100% random.

For the second 1 million IOPS per VM test, the setup used 2 x Violin Memory 6616 Flash Memory Arrays with the below setup.

  • Hypervisor: vSphere 5.1
  • Server: HP DL380 Gen8
    CPU: 2 x Intel Xeon E5-2690, HyperThreading disabled
    Memory: 256GB
  • HBAs: 5 x QLE2562
  • Storage: 2 x Violin Memory 6616 Flash Memory Arrays
  • VM: Windows Server 2008 R2, 8 vCPUs and 48GB.
    Iometer Config: 4K IO size w/ 16 workers

For both configurations, all I/O needs to traverse from the VM, through the hypervisor, out HBAs/NICs, across a storage area network, through central controllers and then make the return journey back to the VM.

There is so many places where additional latency or contention can be introduced in the storage stack it’s amazing VMs can produce the level of storage performance they do, especially back 3 years ago.

Chad Sakac wrote a great article back in 2009 called “VMware I/O Queues, Microbursting and Multipathing“, which has the below representation of the path I/O takes between a VM and a centralized SAN.

6a00e552e53bd28833011570408872970c

As we can see, Chad shows 12 steps for I/O to get to the disk queues, and once the I/O is completed, the I/O needs to traverse all the way back to the VM, so all in all you could argue it’s a 24 step round trip for EVERY I/O!

The reason I am pointing this out is because the argument around “In-kernel” verses “Virtual Storage Appliance” is only about 1 step in the I/O path, when Hyper-Converged solutions like Nutanix (which uses a VSA) eliminate 3/4’s of the steps in an overcomplicated I/O path which has been proven to achieve 1 million IOPS per VM.

Andre Leibovici recently wrote the article “Nutanix Traffic Routing: Setting the story straight” where he shows the I/O path for VMs using Nutanix.

The below diagram which Andre created shows the I/O path (for Read I/O) goes from the VM, across the ESXi hypervisor to the Controller VM (CVM) which then using DirectPath I/O to directly access the locally attached SSD and SATA drives.

nutanix_datapath3

Consider if the VM in the above diagram was a Web Server and the CVM was a database server and they were running in an environment with a SAN/NAS. The Web Server would be communicating to the DB server over the network (via the hypervisor) but the DB Server would have to access it’s data (that the Web Server requested) from the centralized SAN, so in the vast majority of environments today (which are using SAN/NAS) the data is travelling a much longer path than it would compared to a VSA solution and in many cases traversing from one VM to another across the hypervisor before going to the SAN/NAS and back through a VM to be served to the VM requesting the data.

Now back to the diagram, For Nutanix the Read I/O under normal circumstances will be served locally around 95% of the time, this is thanks to data locality and how Write I/O happens.

For Write I/Os, one copy of each piece of data is written locally where the VM is running which means all subsequent Read I/O can be served locally (and freshly written data is also typically “Active data”), and the 2nd copy is replicated throughout the Nutanix cluster. This means even though half the Write I/O (of the two copies) needs to traverse the LAN, it doesn’t hit a choke point like a traditional SAN, because Nutanix scales out controllers on a 1:1 ratio with ESXi hosts and writes are distributed throughout the cluster in 1MB extents.

So if we look back to Chad’s (awesome!) diagram, Hyper-converged solutions like Nutanix and VSAN are only concerned with Steps 1,2,3,12 (4 total) for Read I/O and 1,2,3,12 as well as 1 step for the NIC at the source & 1 step for the NIC at the destination host.

So overall it’s 4 steps for Read, 6 steps for Write, compared to 12 for Read and 12 for Write for a traditional SAN.

So Hyper-converged solutions regardless of In-Kernel or VSA based remove many of the potential points of failure and contention compare to a traditional SANNAS and as a result, have MUCH more efficient data paths.

On twitter recently, I responded to a tweet where the person claims “Hyperconverged is about software, not hardware”.

I disagree, Hyper-converged to me (and the folk at Nutanix) is all about the customer experience. It should be simple to deploy, manage, scale etc, all of which constitute the customers experience. Everything in the datacenter runs on HW, so I don’t get the fuss on the Software only vs Appliance / OEM software only solution debate either, but this is a topic for another post.

TweetAboutCustomerExperience

I agree doing things in software is a great idea, and that is what Nutanix and VSAN do, provide a solution in software which combines with commodity hardware to create a Hyper-converged solution.

Summary:

A great customer experience (which is what I believe matters) along with high performance (1M+ IOPS) solution can be delivered both In-Kernel or via a VSA, it’s simple as that. We are long past the days where a VM was a significant bottleneck (circa 2004 w/ ESX 2.x).

I’m glad VMware has led the market in pushing customers to virtualize Business Critical Apps, because it works really really well and delivers lots of value to customers.

As a result of countless best practice guides, white papers, case studies from VMware and VMware Storage Partners such as Nutanix, we know highly compute / network & storage intensive applications can easily be virtualized, so anyone saying a Virtual Storage Appliance can’t (or shouldn’t) be, simply doesn’t understand how efficient the ESXi hypervisor is and/or he/she hasn’t had the industry experience deploying storage intensive Business Critical Applications.

To all Hyper-converged vendors: Can we stop this ridiculous debate and get on with the business of delivering a great customer experience and focus on the business at hand of taking down traditional SAN/NAS? I don’t know about you, but that’s what I’ll be doing.