Wednesday, November 14, 2012

Clustered Shared Volumes (2.0) in Windows Server 2012

Clustered Shared Volumes was first introduced in Windows Server 2008 R2, and was almost as popular as sliced bread by the time. A great enhancement, and it was solely meant for Hyper-V virtual machines.

Instead of using a dedicated LUN for each VM (so that you could migrate them between cluster nodes without taking down the other VMs on the same LUN) as in Windows Server 2008, you had now the possibility to store multiple VMs on the same LUN by converting it to CSV.

CSV is a distributed file access solution that let multiple nodes in a cluster to access the same file system simultaneously.

This means that many VMs can share the same volume, while you can failover, live migrate and move VMs without affecting the other virtual machines. This leads to better utilization of your storage since you don’t have to place VMs on separate disks, and the CSV’s are not depending in disk letters so you can scale this configuration out, if you’d like.

What’s the latest and greatest related to CSV 2.0:


·         Windows Server 2012 has brought some changes to the architecture, so there’s now a new NTFS compatible file system, which is called CSVFS. This means that applications running on a CSV are able to discover this, and leverage this. But still, the underlying file system is NTFS.


·         BitLocker Support is added to the list, which means you can secure your CSVs on a remote location. The Cluster Name Object is used as the identity to decryption and you should include this in every cluster deployment you are doing, because the performance penalty are less than 1%.


·         Direct I/O for data access which gives enhancements for virtual machine creation and copy operations.


·         Support for other roles than Virtual Machines. There’s an entirely new story around SMB in Windows Server 2012, and CSV is also affected by this. You can now put a SMB file share on top of your CSVs, which makes it easier to scale out your cluster storage, to share a single CSV among several clusters, where they will access their shares instead of volumes. Just a reminder: You can run Hyper-V virtual machines from a SMB file share in Windows Server 2012. This requires that both the server and the client is using SMB 3.0.


·         The marriage to Active Directory has come to an end. External authentication dependencies, which you would run into if you started your cluster without an available AD is now removed. This gives us an easier setup of clusters, with less trouble and dependencies.


·         File backup by supporting requestors that’s running Windows Server 2008 R2 or 2012. You can use application consistent and crash consistent VSS snapshots.


·         SMB support with multichannel and direct. CSV traffic can now stream across multiple networks in the clusters and utilize the performance in your NICs that supports RDMA.


·         Integration with storage spaces (new in Windows Server 2012) so that you can leverage your cheap disks (just a bunch of disks, JBOD) in a cluster environment


·         Maintenance by scanning and repairing volumes with no downtime

Although there’s several enhancement for VM mobility in 2012, where you can move VMs without shared storage, there are still significant benefits by clustering your Hyper-V hosts.

Remember: No cluster = no high availability.


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