Part 5.4 - Cluster Shared Volumes

Sorry about the delay in continuing my series.  In the time I was away, I attended TechEd (always an impressive show) and got wrapped up with two different clients.  All good things but I got a bit distracted.  But here is the next installment of the Windows Server 2012 goodness – cluster shared volumes.

If you aren’t familiar with CSVs, see this excellent post on TechNet for the full scoop.  The basic rendition is this:  let’s say you have a cluster of machines and you want to have common storage among all of the instances.  This common storage would be used for like SQL Clusters, file server clusters, etc.  The problem with CSVs were many, but the main culprits were: they only worked with certain workloads, they were hard to configure and often broke (typically around patch Tuesday when the head node rebooted).

In Windows 2012, one of the foundational underpinnings of all that is good is storage (hence the sub series on just this).  In 2012, like 2008R2, we have the ability to create CSVs for the Hyper-V role.  This means that all of my hosts can share a common storage LUN (or SMB3 but that’s another post!) and hosts only write to the blocks they are supposed to because they are smart (they know which VMs are being run in the cluster by which host).  The obvious benefit is that when you need to live migrate from one host to another in the same cluster, all you do is transfer the memory and bam, you’re done.  No more LUN remapping which I swear never really worked anyways.  CSVs have also been extended now to the file server role, which brings in impressive additional capabilities.  But they didn’t stop there.

CSVs in 2012 are even more impressive when you combine cluster aware patching as described earlier as well as drain stopping clusters, taking host nodes into a maintenance mode and particularly with regard to backups.  I don’t fully understand the changes to the VSS writers within Windows to fully appreciate all that was done here but I do know that backups are now much smarter and less impactful on storage arrays when snapshots need to be taken.

Here is a list of other goodies that CSVs (along with Clustering services in general) bring to the table in Windows 2012:

1. Bitlocker support for the CSV
2. 63 host nodes per cluster
3. 4000 VMs per cluster
4. Continuous availability for storage
5. Parallel backups support
6. Better incremental and snapshot support

Finally, CSVs can also take advantage of other general storage enhancements that are amazing as well:

1. Data deduplication
2. New file system which supports way bigger drives and more efficient storage (4KB sectors)
3. Encrypted hard drive support (full hardware offloading of Bitlockering)
4. Support for ODX (Offline Data Transfer) which, if you haven’t seen, checkout the Day 1 Keynote of TechEd North America to see them use ODX to transfer data at 10 GIGABYTES per second (not gigabits…GIGABYTES)
5. Full support for the SMI-S protocol so that Windows can talk directly to storage arrays and carve up LUNs and more.  Very useful to System Center.

If you are a nerd like me, you will love CSVs and clustering in general in 2012.  It is the key to a flexible cloud…well, one of them.  Tune in next time where I’ll talk about something completely different maybe!