As you would probably know, as a regular reader of this blog, Active Directory Domain Services performs a storage trick to prevent corruption in the Active Directory database. It does this by disabling write-back caching on the physical spindle where the Active Directory database resides. This way, the Domain Controller asks the storage device to write the data to disk instead of a cache module on the storage controller.
Now, when you virtualize a Domain Controller, the Windows Server Operating System will disable write-back caching on the virtual hard disk (*.vhd or *.vhdx), instead of the physical spindle. Just as in the physical world, the virtual Domain Controller asks the storage device to write the data to disk instead of cache (whether virtual or physical).
When a virtual Domain Controller is running on Hyper-V in Windows Server 2012 R2, the hypervisor is aware of the virtual machine requesting writing data to disk.
When you’re using Hyper-V in Windows Server 2012 R2 in combination with Storage Spaces with Storage Tiering, this latter feature from Windows Server 2012 R2 dedicates a slice of storage from its fastest storage tier (for instance, SSD storage when SSD Tiering) as disk space for the Active Directory database. This way, the Hyper-V host will commit changes to storage fast, just as the virtual machine asked.
Afterwards, during the processing the heat map, the slice of storage used to store the data for the virtual hard disk of virtual Domain Controller with write-back caching enabled, is transferred to a slower storage tier (where applicable).
This feature dramatically improves the performance of virtual Domain Controllers running on Hyper-V in Windows Server 2012 R2 with Storage Spaces with Storage Tiering.
Storage Tiering is a feature your virtual Domain Controllers will benefit from hugely.
Use SSD Tiering or Write-Back Cache with Windows Server 2012 R2 Storage Space
Windows Server 2012 R2 Beefs Up Storage Spaces
The Effects Of WS2012 R2 Storage Spaces Write-Back Cache On A Hyper-V VM
Permalink to- The Effects Of WS2012 R2 Storage Spaces Write-Back Cache
[VIDEO] Storage Spaces: What’s New in Windows Server 2012 R2
Thanks to Aidan Finn for pointing me to this new unctionality.