Category Archives: IT Pro

Confusing Mellanox Windows PerfMon Counters

Posted on by
6

Introduction

So you start out doing SMB Direct. Maybe you’re doing RoCE, if so there’s a good chance you’ll be using the excellent Mellanox cards. You studied hard, read a lot and put some real effort into setting it up. The SMB Direct / DCB configuration is how you think it should be and things are working as expected.

Curious as you are you want to find out if you can see Priority Flow Control work. Well, the easiest way to do so is by using the Windows Performance Monitor counters that Mellanox provides.

Confusing Mellanox Windows PerfMon Counters

So you take your first look at the Mellanox Adaptor QoS Perfmon counters for ConnectX series for SMB Direct (RDMA) traffic. When you want to see what’s happening in regards to pause frames that have been sent and received and what pause duration was requested from the receiving hop (or received from the sending hop) you can get confused. The naming is a bit counter intuitive.

clip_image002

The Rcv Pause duration is not the duration requested by the pause frames the host received, but by the pause frames that host sent. Likewise, the Sent Pause duration is not the duration requested by the pause frames the host send, but by the pause frames that host received.

clip_image004

So you might end up wondering why your host sends pause frames but to only see the Rcv Pause duration go up. Now you know why Smile.

Now there were plans to fix this in WinOF 4.95. The original release note made mention of this and this made me quite happy as most people are confused enough when it comes to RDMA/RoCE/DCB configurations as it is.

A screenshot of the change in the original Mellanox WinOF VPI Release Notes revision 4.95

clip_image005

Unfortunately, this did not happen. It was removed in a newer version of these release notes. My guess is it could have been a breaking chance of some sort if a lot of tooling or automation is expecting these counter names.

I still remember how puzzled I looked at the counters which to me didn’t make sense and the tedious labor of empirical testing to figure out that the wording was a bit “less than optimal”.

But look, once you know this you just need to keep it in mind. For now, we’ll have to live with some confusing Mellanox Windows PerfMon counter names. At least I hope I have saved you the confusion and time I went through when first starting with these Mellanox counters. Other than that I can only say that you should not be discouraged as they have been and are a great tool in checking RoCE DCB/PFC configs.

Maximum bandwidth in Hyper-V storage QoS policies

Posted on by
Reply

Introduction

In a previous blog post Hyper-V Storage QoS in Windows Server 2016 Works on SOFS and on LUNs/CSV I have discussed Storage QoS Policies in Windows Server 2016. I have also demonstrated this in a lab setup at VEEAMON 2015 in one of my talks at the Microsoft presentation area. It’s one of those features where a home lab will do the job. There is no need for special storage hardware. It’s all in box functionality. Cool!

Maximum bandwidth in Hyper-V storage QoS policies

Now that was in the Technical Preview 2 and 3 era, where it all revolved around minimum and maximum QoS. In Windows Server 2016 Technical Preview 4 we got some new features in regards to storage QoS policies. One of those is that we can now also set the Maximum bandwidth on a policy using the parameter MaximumIOBandwidth. This parameter, which is set in bytes per second determines the maximum bandwidth that any flow assigned to the policy is allowed to consume.

image

We use that policy ID to assign it to the 2 shared virtual disks of our cluster nodes. You’ll need to do this for all of the guest cluster nodes.image

You can copy the PoSh demo script below

[sourcecode language=”powershell”]

#Create a Storage Policies
$DemoVMPolicy = New-StorageQosPolicy -Name DemoVMPolicy -PolicyType MultiInstance `
-MinimumIops 250 -MaximumIops 500 -MaximumIOBandwidth 100MB

#Look at our storage Policies
Get-StorageQosPolicy -name DemoVMPolicy

#Grab our policy ID
$DemoVMPolicy = (get-StorageQosPolicy -Name DemoVMPolicy).PolicyId
$DemoVMPolicy

#Look at our VMs policy setting before and after assigning a storage policy.
#We assign the storage policy to the 2 shared virtual disks
#that are located a location 1 and 2 on SCSI controller 0

Get-VM -Name GuestClusterNode1 | Get-VMHardDiskDrive |
ft Path,MinimumIOPS, MaximumIOPS, MaximumIOBandwidth, QoSPolicyID -AutoSize

Get-VM -Name GuestClusterNode1 | Get-VMHardDiskDrive | Where-Object {$_.controllerlocation -ge 1}|
Set-VMHardDiskDrive -QoSPolicyID $DemoVMPolicy

Get-VM -Name GuestClusterNode1 | Get-VMHardDiskDrive |
ft Path, MinimumIOPS, MaximumIOPS, MaximumIOBandwidth, QoSPolicyID -AutoSize
[/sourcecode]

You can use MaximumIOBandwidth by itself or you can combine it with the maximum IOPS setting. When both of these parameter are set in a storage QoS policy they are both active. The one that is reached first by a flow assigned to this policy will be the limiting factor in the I/O of that flow.

As an example. Let’s say you specify 500 IOPS and 100Mbps bandwidth as maxima. Your workload hits 500 IOPS but only consumes 58 Mbps it’s the IOPS that are limiting the flow.

Load balancing UDP for a RD Gateway farm with a KEMP Loadmaster

Posted on by
5

When implementing load balancing for RD Gateway we must take care not to forget load balancing the UDP traffic. Now your RDP Connection will still work over HTTPS alone if you forget this, but you’ll miss out on the benefits.

  • Better experience of bad, unreliable network connections with high packet loss
  • Better experience with high end graphics and in general a better graphical experience over WAN links.

As many people have load balanced their gateways since Windows Server 2008 (R2) when UDP was not into play yet and as things work without people might forget. The most important thing you need to know is that when leveraging UDP for RDP 8/8.1 the UDP session traffic has to leverage Direct Server Return (DSR) for the real servers configuration when we configure load balancing for a RD gateway farm with a KEMP Loadmaster. I’m focusing on the UDP part here, not the HTTPS part. That’s been done enough and the Kemp info on that is sufficient. The UDP part could do with some extra info.

The reason for this is that when UDP is leveraged for high end graphics we want to avoid sending all that graphical network traffic the load balancer. There is no real added value being performed there in this UDP use case but the load might get quite high. This is where DSR is leveraged wen configuring the Loadmaster. That means we also need to configure our real servers to uses Direct Return as the forwarding method. When you forget this you’ll lose UDP with RDP 8.1 but you might not notice immediately. If you’re not looking for it as the HTTP connection alone will let you connect and work, albeit with a reduced experience.

To read more on why it’s done this way (even if it seems complex and has drawbacks) see http://kemptechnologies.com/ca/white-papers/direct-server-return-it-you/ you’ll notice that for graphics it is great idea. By selecting Direct Server Return as the  forwarding method (see later) changes the destination MAC address of the incoming packet on the fly (very fast) to the MAC address of one of the real servers. When the packet reaches the real server it must think it owns the VS IP address, which it doesn’t. So we use the loopback adapter to let the real server reply as if it does but we don’t respond to ARPs as that would cause issues with the load balancer who has the real IP of the virtual service. That’s where the 254 metric we configure in the demo below comes into play.  Note that  the real server responds over it normal NIC. Which is great and it helps with firewall rules not ruining the party. That’s why with DSR which leverages the the loopback adapter on the RD Gateway servers also requires you to configure the weak host / strong host behavior for the network configuration on those servers, it’s not answering itself! I’ll not go into details on this here but basically since Windows Vista and Windows Server 2008 the security model has change from weak host to strong host. This means that a system (that is not acting as a router) cannot send or receive any packets on a given interface unless the destination/source IP in the packet is assigned to the interface. In the “weak host” model, this restriction does not apply. Read more about this here. Let’s walk through this UDP/DSR/weak host setup & configuration.

On your Loadmaster you’ll create a virtual service for UDP traffic.

  • Select Virtual Services > Add New.
  • Enter the IP address of your RD Gateway Farm
  • Set 3391 as the Port.
  • Select udp for the Protocol.
  • Click Add this Virtual Service.

Open up the Standard Options to configure those

image

  • We don’t need layer 7 as the UDP connections are tied to the HTPP connection and they will spawn and die with that one.
  • We select Source IP Address as the Persistence Mode as the RD Gateway needs persistence to guarantee the connection stay together on the same RD Gateway server. Set the time out value no to high so it isn’t remembered to long.
  • We select least connections as that’s the best option in most cases, let the farm node with the least load take on new connections. This is handy after down time for example.

Now head over to the Real Servers section

image

  • Make sure the Real Server Check parameters is set to ICMP ping, which is what the LoadMaster uses to check if the RD Gateway servers are alive.
  • Click Add New to add an  RD Gateway server, you’ll do this for each farm member.

image

  • Enter the Real Server Address for each RD Gateway.
  • Enter 3391 as the Port.
  • Select Direct return as the Forwarding method.
  • Click Add This Real Server.

When you’re done it looks like this:

image

So now we need to check if the real servers are seen as on line and healthy …

image

If one RD Gateway server is down or has an issue you see this … no worries the LoadMaster sends all clients to the other farm member server.

image

Configure the  RD Gateway farm servers to work with DSR

We’re not done yet, we need to configure our RD Gateway servers in the farm to work with DSR.

Go to Device Manager, right-click on the computer name and select Add legacy hardware

image

Click next on the welcome part of the wizard …

image

Select “Install the hardware that I manually select from a list (Advanced)” and click Next …image

Scroll down to network adapters, select it and click Next …image

Under Manufacturer choose Microsoft and as Network Adapter scroll down to Microsoft KM-TEST Loopback Adapter, select it and click Next.

image

Click Next to install it …image

image

Click next to close the Wizard.image

 

Now go to  and change the name so you can easily identify the loopback adapter …imageimage

In the properties of the loopback adapter we disable everything we don’t need. In this case, we only need IPV4 and nothing else. We also need to configure the TCP/IP settings for the loopback adapter. So open up the TCP/IP v4 properties of that NIC …image

Enter the IP address of the Virtual Service for UDP on the load master and, very important enter a subnet mask of 255.255.255.255 for the loopback address. It’s a subnet of 1 host, the VIP IP address. Do not enter a gateway!

image

Now go to the advanced setting and deselect Automatic metric and fill out 254. This step prevents the server to respond to ARP requests for the MAC of the VIP with the MAC of the loop back adapter.

image

Also uncheck “Register this connection”s address in DNS” to avoid any name resolution problems for the real servers.

image

Finally disable NETBIOS over TCP/IP.

image

What we are doing with all the above is preventing any issues with normal network traffic to this real servers being affected by the loopback adapter who’s one and only function is to enable DSR and nothing else. It’s a bit “paranoid” but it pays to be and prevent problems.

Dealing with Strong Host / Weak Host setting in W2K8 and higher

We now still need to deal with the strong host security model and allow the LAN interface to receive traffic from the KEMP and allow the KEMP to receive and send traffic form/to the LAN interface. This is done by executing the following commands:

netsh interface ipv4 set interface LAN weakhostreceive=enabled
netsh interface ipv4 set interface KEMP-DSR-LOOPBACK weakhostreceive=enabled
netsh interface ipv4 set interface KEMP-DSR-LOOPBACK weakhostsend=enabled

That’s it. You should now have HTTP/UDP connections in your RD Gateway monitoring when using a load balancer and set it up correctly.  Remember if this isn’t configured correctly you’ll still connect but you lose the benefits the UDP connections offer.

Now another thing you need to be aware of in your RD Gateway configuration is that for UDP  to work with DSR is that the UDP Transport Settings need to be configured for “all unassigned” IP addresses. Other wise DRS won’t work and you’ll lose UDP. This make sense, you’ll receive traffic on the VIP on your real servers. It’s just like DSR with a web server where in IIS you’ll bind both the LAN and the loopback adapter to port 80 or 443 for the site.

image

We can see that one client is connected via RDSGW01 to two servers (Viking and Spartan) leveraging HTTP and UDP. The load balancing is done via the KEMP Loadmasters in  geo-redundant fashion.

image

Yes, my geo load balanced RD Gateway Server farms are providing UDP support for the servers and clients we  RDP in to.

image

Combined with those servers and clients being spread amongst the sites provides for enough business continuity to keep the shop running when a site fails, so it’s more than just connectivity!

A first look at shared virtual disks in Windows Server 2016

Posted on by
2

Introduction to shared virtual disks in Windows Server 2016

Time to take a first look at shared virtual disks in Windows Server 2016 and how they are set up. Shared VHDX was first introduced in Windows Server 2012 R2. It provides shared storage for use by virtual machines without having to “break through” the virtualization layer. This way is still available to us in Windows Server 2016. The benefit of this is that you will not be forced to upgrade your Windows Server 2012 R2 guest clusters when you move them to Windows Server 2016 Hyper-V cluster hosts.

The new way is based on a VHD Set. This is a vhds virtual hard disk file of 260 MB and a fixed or dynamically expanding avhdx which contains the actual data. This is the “backing storage file” in Microsoft speak. The vhds file is used to handle the coordination of actions on the shared disk between the guest cluster nodes?

Note that an avhdx is often associated with a differencing disk or checkpoints. But the “a” stands for “automatic”. This means the virtual disk file can be manipulated by the hypervisor and you shouldn’t really do anything with it. As a matter of fact, you can rename this off line avhdx file to vhdx, mount it and get to the data. Whether this virtual disk is fixed or dynamically expanding doesn’t matter.

You can create on in the GUI where it’s just a new option in the New Virtual Hard Disk Wizard.

Or via PowerShell in the way you’re used to with the only difference being that you specify vhds as the virtual disk extension.

In both cases both vhds and avhdx are created for you, you do not need to specify this.

You just add it to all nodes of the guest cluster by selecting a “Shared Drive” to add to a SCSI controller …

… browsing to the vhds , selecting it and applying the settings to the virtual machine. Do this for all guest cluster nodes

Naturally PowerShell is your friend, simple and efficient.

Rules & Restrictions

As before shared virtual disk files have to be attached to a vSCSI controller in the virtual machines that access it and it needs to be stored on a CSV. Both block level storage or a SMB 3 file share on a Scale Out File Server will do for this purpose. If you don’t store the shared VHDX or VHD Set on a CSV you’ll get an error.

Sure for lab purposes you can use an non high available SMB 3 share “simulating” a real SOFS share but that’s only good for your lab or laptop.

The virtual machines will see this shared VHDX as shared storage and as such it can be used as cluster storage. This is an awesome concept as it does away with iSCSI or virtual FC to the virtual machines in an attempt to get shared storage when SMB 3 via SOFS is not an option for some reason. Shared VHDX introduces operational ease as it avoids the complexities and drawbacks of not using virtual disks with iSCSI or vFC.

In Windows Server 2012 R2 we did miss some capabilities and features we have come to love and leverage with virtual hard disks in Hyper-V. The reason for this was the complexity involved in coordinating such storage actions across all the virtual machines accessing it. These virtual machines might be running on different hosts and, potentially the shared VHDX could reside on different CSVs. The big four limitations that proved to be show stopper for some use cases are in my personal order of importance:

  1. No host level backup
  2. No on line dynamic resize
  3. No storage live migration
  4. No checkpoints
  5. No Hyper-V Replica support

I’m happy to report most of these limitations have been taken care of in Windows Server 2016. We can do host level backups. We can online resize a shared VHDX and we have support for Hyper-V replica.

Currently in 2016 TPv4 storage live migration and checkpoints (both production and standard checkpoints) are still missing in action but who knows what Microsoft is working on or has planned. To the best of my knowledge they have a pretty good understanding of what’s needed, what should have priority and what needs to be planned in. We’ll see.

Other good news is that shared VHDX works with the new storage resiliency feature in Windows Server 2016. See Virtual Machine Storage Resiliency in Windows Server 2016 for more information. Due to the nature of clustering when a virtual machine loses access to a shared VHDX the workload (role) will move to another guest cluster node that still has access to the shared VHDX. Naturally if the cause of the storage outage is host cluster wide (the storage fabric or storage array is toast) this will not help, but other than that it provides for a good experience. The virtual machine guest cluster node that has lost storage doesn’t go into critical pause but keeps polling to see if it regains access to the shared VHDX. When it does it’s reattached and that VM becomes a happy fully functional node again.

It also supports the new Storage Qos Policies in Windows Server 2016, which is something I’ve found during testing.

Thanks for reading!