Hyper V Archives - Page 3 of 3 - SIOS SANless clusters

There has recently been a lot of press, about executing virtual machines live migrations across long-distanced data centers, that herald VMware’s limited support for vMotion across Data Centers, or “long-distance vMotion” as I have seen it called. The details of the solution can be found on Cisco’s website here. While I think that is just great, I’d like to remind people that Microsoft Hyper-V has this same functionality today and has a lot less requirements and restrictions than VMware’s long-distance vMotion.

Where VMware has VMwareHA, vMotion and Site Recovery Manager (SRM) to take care of virtual machine availability, Microsoft provides the same functionality with Windows Server Failover Clustering and in fact in some cases goes beyond what VMware can provide in terms of virtual machine availability as I described in a previous post.

What I’d like to focus on today is Microsoft’s competitive offering to “long-distance vMotion”. To achieve the same functionality in Hyper-V, you simply deploy a multi-site Hyper-V cluster using Windows Server Failover Clustering and your favorite host or storage based replication solution that is certified to work in a Windows Server 2008 multi-site cluster. By doing this, you can use your existing network infrastructure and your existing storage infrastructure to do Live Migrations across data centers. As far as requirements, they really are the same as any multi-site cluster, except I would recommend that you span your subnets to avoid client reconnection issues that occur when moving a virtual machine to a new subnet, as the clients could cache to old IP address until the TTL expires.

A demonstration video of Live Migration across data centers using Windows Server 2008 R2 Hyper-V and SteelEye DataKeeper Cluster Edition can be seen here.

Reproduced with permission from https://clusteringformeremortals.com/2009/09/17/hyper-v-live-migration-across-data-centers/

With the release of Windows Server 2008 R2, one of the enhancements was improving the performance of dynamic VHD files. Prior to R2, writes to dynamically expanding VHD files could be 3x slower than writes to a fixed size VHD file due to limited meta data caching. Overall, Microsoft is claiming the performance of dynamic VHD files vs. fixed size VHD files is almost identical.Pass-through disks are another option when configuring a Hyper-V VM. According to my results, the performance of a pass-through disk is marginally better than that of VHD files. However, if you use pass-through disks you lose all of the benefits of VHD files such as portability, snap-shotting and thin provisioning. Considering these trade-offs, using pass-through disks should really only be considered if you require a disk that is greater than 2 TB in size or if your application is I/O bound and you really could benefit from another .1 ms shaved off your average response time.

I figured rather than taking Microsoft’s word for it, I would put these different disk types to the test for myself. I set up a Hyper-V Windows Server 2008 R2 virtual machine running on top of Windows Server 2008 R2. For my Hypervisor, I used Dell PowerEdge 1950 server attached to a Dell AX150 SAN and carved off three 10 GB LUNs for use in my test. In Hyper-V Manager, I added three new disks, one pass-through, one dynamic VHD and one fixed-size VHD. I then used IOMeter to test the performance of the disks. The test parameters and raw data can be found in this CSV file.

The charts below summarize my results. As you can see, on the extremes (Maximum/Minimum), the pass-through disk wins in most cases. However, on average, there is almost no difference between the performances of the three different disk types.

Performances of the three different disk types -Dynamic VHD, Fixed Size VHD, Pass-Through

The benefit of thin provisioning, meaning building a VHD file or multiple VHD files with a combined size that is greater than the available disk space, and the portability of VHD files make dynamically expanding VHD files the obvious choice for most Windows Server 2008 R2 virtual machines.

In summary, I’d strongly consider the use of dynamically expanding VHD files for your next Hyper-V deployment on Windows Server 2008 R2.

Reproduced with permission from https://clusteringformeremortals.com/2009/09/25/hyper-v-pass-through-disk-performance-vs-fixed-size-vhd-files-and-dynamic-vhd-files-in-windows-server-2008-r2/