Category Archives: Clustering

Integration Services Version Check Via Hyper-V Integration/Admin Event Log

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I’ve written before (see "Key Value Pair Exchange WMI Component Property GuestIntrinsicExchangeItems & Assumptions") on the need to & ways with PowerShell to determine the version of the integration services or integration components running in your guests. These need to be in sync with the one running on the hosts. Meaning that all the hosts in a cluster should be running the same version as well as the guests.

During an upgrade with a service pack this get the necessary attention and scripts (PowerShell) are written to check versions and create reports and normally you end up with a pretty consistent cluster. Over time virtual machines are imported, inherited from another cluster of created on a test/developer host and shipped to production. I know, I know, this isn’t something that should happen, but I don’t always have the luxury of working in a perfect world.

Enough said. This means you might end up with guests that are not running the most recent version of the integration tools. Apart from checking manually in the guest (which is tedious, see my blog "Upgrading a Hyper-V R2 Cluster to Windows 2008 R2 SP1" on how to do this) or running previously mentioned script you can also check the Hyper-V event log.

Another way to spot virtual machines that might not have the most recent version of the integration tools is via the Hyper-V logs. In Server Manager you drill down in the “Diagnostics” to, “Event Viewer” and than navigate your way through  "Applications and Services Logs", "Microsoft", "Windows" until you hit “Hyper-V-Integration”

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Take a closer look and you’ll see the warning about 2 guests having an older version of the integration tools installed.

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As you can see it records a warning for every virtual machine whose integration services are older than the host running Hyper-V. This makes it easy to grab a list of guest needing some attention. The down side is that you need to check all hosts, not to bad for a small cluster but not very efficient on the larger ones.

So just remember this as another way to spot virtual machines that might not have the most recent version of the integration tools. It’s not a replacement for some cool PowerShell scripting or the BPA tools, but it is a handy quick way to check the version for all the guests on a host when you’re in a hurry.

It might be nice if integration services version management becomes easier in the future. Meaning a built-in way to report on the versions in the guests and an easier way to deploy these automatically if there not part of a service pack (this is the case when the guest OS and the host OS differ or when you can’t install the SP in the guest for some application compatibility reason). You can do this in bulk using SCVMM and of cause Scripting this with PowerShell comes to the rescue here again, especially when dealing with hundreds of virtual machines in multiple large clusters. Orchestration via System Center Orchestrator can also be used. Integration with WSUS would be another nice option, for those that don’t have Configuration Manager or Orchestrator but that’s not supported as far as I know for now.

Know What Receive Side Scaling (RSS) Is For Better Decisions With Windows 8

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Introduction

As I mentioned in an introduction post Thinking About Windows 8 Server & Hyper-V 3.0 Network Performance there will be a lot of options and design decisions to be made in the networking area, especially with Hyper-V 3.0. When we’ll be discussing DVMQ (see DMVQ In Windows 8 Hyper-V), SR-IOV in Windows 8 (or VMQ/VMDq in Windows 2008 R2) and other network features with their benefits, drawbacks and requirements it helps to know what Receive Side Scaling (RSS) is. Chances are you know it better than the other mentioned optimizations. After all it’s been around longer than VMQ or SR-IOV and it’s beneficial to other workloads than virtualization. So even if you’re a “hardware only for my servers” die hard kind of person you can already be familiar with it. Perhaps you even "dislike” it because when the Scalable Networking Pack came out for Windows  2003 it wasn’t such a trouble free & happy experience. This was due to incompatibilities with a lot of the NIC drivers and it wasn’t fixed very fast. This means the internet is loaded with posts on how to disable RSS & the offload settings on which it depends. This was done to get stability or performance back for application servers like Exchange and others applications or services.

The Case for RSS

But since Windows 2008 these days are over. RSS is a great technology that gets you a lot better usage of out of your network bandwidth and your server. Not using RSS means that you’ll buy extra servers to handle the same workload. That wastes both energy and money. So how does RSS achieve this? Well without RSS all the interrupt from a NIC go to the same CPU/Core in multicore processors (Core 0).  In Task Manager that looks not unlike the picture below:

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Now for a while the increase in CPU power kept the negative effects at bay for a lot of us in the 1Gbps era. But now, with 10Gbps becoming more common every day, that’s no longer the case. That core will become the bottle neck as that poor logical CPU will be running at 100%, processing as much network interrupts in can handle, while the other logical CPU only have to deal with the other workloads. You might never see more than 3.5Gbps of bandwidth being used if you don’t use RSS. The CPU core just can’t keep up. When you use RSS the processing of those interrupts is distributed across al cores.

With Windows 2008 and Windows 2008 R2 and Windows 8 RSS is enabled by default in the operating system. Your NIC needs to support it and in that case you’ll be able to disable or enable it. Often you’ll get some advanced features (illustrated below) with the better NICs on the market. You’ll be able to set the base processor, the number of processors to use, the number of queues etc. That way you can divide the cores up amongst multiple NICs and/or tie NICs to specific cores.

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So you can get fancy if needed and tweak the settings if needed for multi NIC systems. You can experiment with the best setting for your needs, follow the vendors defaults (Intel for example has different workload profiles for their NICs) or read up on what particular applications require for best performance.

Information On How To Make It Work

For more information on tweaking RSS you take a look at the following document http://msdn.microsoft.com/en-us/windows/hardware/gg463392. It holds a lot more information than just RSS in various scenarios so it’s a useful document for more than just this.

Another good guide is the "Networking Deployment Guide: Deploying High-Speed Networking Features". Those docs are about Windows 2008 R2 but they do have good information on RSS.

If you notice that RSS is correctly configured but it doesn’t seem to work for you it’ might be time to check up on the other adaptor offloads like TCP Checksum Offload, Large Send Offload etc. These also get turned of a lot when trouble shooting performance or reliability issues but RSS depends on them to work. If turned off, this could be the reason RSS is not working for you..

KB 2636573: Guest Crashes with Win2008R2 RTM/SP1 STOP 0xD1 in storvsc!StorChannelVmbusCallback During Live Migration

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The BSOD

I helped hunt down this bug and tested the private fix. Some months ago, during the summer of 2011, I was putting some new Hyper-V clusters under stress tests. You know, letting it work very hard for a longer period of time to see if anything falls off or goes “boink". It all looked pretty robust and and after some tweaking also very fast. Just when you’re about to declare “we’re all set” here you see a BSOD on one of the guests that’s being live migrated happily announcing: “DRIVER_IRQL_NOT_LESS_OR_EQUALSTOP: 0x000000D1 (0x0000000000000000, 0x0000000000000000, 0x0000000000000000, 0x0000000000000000)”

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Now that doesn’t make ME very happy however. So I investigate to see if there are any more VMs dropping dead during live migration but we don’t see any. Known issues like out of date versions of the integration tools or the like are not in play nor are any other possible suspects.

We throw the MEMORY.DMP file in the debugger and we come up with the following culprit:

DRIVER_IRQL_NOT_LESS_OR_EQUAL (d1)

The driver probably at fault is storvsc.sys

Probably caused by : storvsc.sys ( storvsc!StorChannelVmbusCallback+2b8 )

Hmmmmmmm, we start searching the internet but we don’t find much. We also throw it on to Twitter to see if the community comes up with something. Meanwhile we keep looking and find this little blog post by a Microsoft support engineer Rob Scheepens:

http://blogs.technet.com/b/dip/archive/2011/10/21/win2008r2-rtm-stop-0xd1-in-storvsc-storchannelvmbuscallback-0x2b5.aspx

We pinged Rob and opened a case with MS support. That evening Hans Vredevoort (www.hyper-v.nu), who saw my tweet, mails me with the details of a fellow MVP in the USA having this same issue. We get in contact an via both Microsoft & the Hyper-V community we start hunting the cause of this bug. The progress on this issue can be read at the Microsoft blog above. You’ll notice that the fix is in the works now.

Hunting down the STOP error

What did we establish:

  • It only happens occasionally with a live migration and it rather ad hoc, not every time, not after X amount of live migrations or X amount of up time.
  • It seems sometimes to happens only with guests running dynamically expanding VHDs attached to ISCSI controllers in Hyper-V.  But that’s not really the case as I remember one being with  fixed VHD attached to an SCSI controller. In our case the VMs we could reproduce the issue with in a reasonable time were all SQL Server test and development guests running SQL Server 2008 where the dynamically expanding disks are used as “poor man’s thin provisioning”.
  • I have not heard of this on Windows 2008 hosts, only R2, but I have not tested this.

So it’s reproducible but it takes intensive live migration activity. Meanwhile we received private instrumentation to install on both guests & hosts to collect “enriched” memory.dumps when a guest experiences a BSOD. With PowerShell we have continuous live migration running to reproduce the issue. The fact that can live migrate over 10Gbps does help Smile. Because you can get lucky but in reality needs many hundreds of live migration to reproduce it. On some machines many thousands. Not a joke but I total we did 8000 Live migrations to test the fix and we did about 12000 to reproduce the issue on several VMs with different configurations to send memory dumps to MSFT. So yes, you really need some PowerShell and having a 10Gbps Live Migration network also helps Winking smile.

All the collected MEMORY.DMP files form these live migration exercises were uploaded to Microsoft for analysis. That took a while, also because they had a boatload of live migrations to do and I don’t know if their test lab has 10 Gbps.

On Tuesday the 25th of October Microsoft contacts us with good news. They have root-caused the problem and a hotfix is in the works. You can download that here http://support.microsoft.com/kb/2636573

On Thursday 27th of October we get access to a private fix and after installing this one we’ve been running thousands of live migrations without  seeing the issue.

The public release of this hotfix is currently planned (HTP11-12) under KB2636573.

The details for the curious

Root Cause?

The root cause can be summarized as follows: “StorVSP was modifying guest memory while the VM’s virtual motherboard was being powered off.” Doing this storvsc access a NULL pointer in a memory buffer that is already freed up. The result of this is a BSOD or STOP error in the virtual machine.

Only SCSI attached VHDs

OK but why do we only see this with SCSI attach VHDs? Now the issue happens during power down of the virtual machines’ mother board because there is a disk enumeration during the shut down phase. And this enumeration only happens with SCSI disks.

Right! So the more VHDs we had attached to SCSI controllers in a virtual machine the higher the likelihood of this happening.

Why so much more likely with dynamically expanding VHDs

But still we saw this exponentially more with dynamically expanding disks. Why is that? Well it’s not that dynamically expanding disks trigger disk enumeration more than fixed disks.  However it seems that any disk expansion, which causes write delays, can lead to a timing issue that will cause the disk enumeration to hit the issue described above. So this significantly increases the risk that the STOP error will happen and it explains that the chance this will happen with fixed VHDs attached to SCSI controllers is significantly lower. This is sync with what we saw. The virtual machines with a lot of dynamic disks attach to SCSI controllers that had a lot of activity (and thus potential for expanding) is the ones where we could reproduce this the fasted.

Conclusion

It can take some time to hunt down certain bugs, especially the rare ones that only happen every now and then so occurrences are few and far between. But when you put in some effort Microsoft helps out and works on a fix. And no you don’t have to have the most expensive support contract for that to happen. As a  matter of fact this call was logged under a free support call with the TechNet Plus subscription. And as it was a bug, they return it as unused.

Anti Virus & Hyper-V Reloaded

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The anti virus industry is both a blessing and a curse.  They protect us from a whole lot of security threats and at the same time they make us pay dearly for their mistakes or failures. Apart from those issues themselves this is aggravated that management does not see the protection it provides on a daily basis. Management only notices anti virus when things go wrong, when they lose productivity and money. And frankly when you consider scenarios like this one …

Hi boss, yes, I know we spent a 1.5 million Euros on our virtualization projects and it’s fully redundant to protect our livelihood. Unfortunately the anti virus product crashed the clusters so we’re out of business for the next 24 hours, at least.

… I can’t blame them for being a bit grumpy about it.

Recently some colleagues & partners in IT got bitten once again by McAfee with one of there patches (8.8 Patch 1 and 8.7 Patch 5). These have caused a lot of BSOD reports and they put the CSVs on Hyper-V clusters into redirected mode (https://kc.mcafee.com/corporate/index?page=content&id=KB73596). Sigh. As you can read here for the redirected mode issue they are telling us Microsoft will have to provide a hotfix. Now all anti virus vendors have their issue but McAfee has had too many issues for to long now.  I had hoped that Intel buying them would have helped with quality assurance but it clearly did not. This only makes me hope that whatever protection against malware is going to built into the hardware will be of a lot better quality as we don’t need our hardware destroying our servers and client devices. We’re also no very happy with the prospect or rolling out firmware & BIOS updates at the rate and with the risk of current anti virus products.

Aidan Finn has written before about the balance between risk & high availability when it comes to putting anti virus on Hyper-V cluster hosts and I concur with his approach:

  • When you do it pay attention to the exclusion & configuration requirements
  • Manage those host very carefully, don’t slap on just any update/patches and this includes anti virus products of cause

I’m have a Masters in biology from they days before I went head over heals into the IT business. From that background I’ve taken my approach to defending against malware. You have to make a judgment call, weighing all the options with their pros and cons. Compare this to vaccines/inoculations to protect the majority of your population. You don’t have to get a 100% complete coverage to be successful in containing an outbreak. Just a sufficiently large enough part including your most vulnerable and most at risk population. Excluding the Hyper-V hosts from mandatory anti virus fits this bill. Will you have 100% success, always? Forget it. There is no such thing.