thing. I would create one availability set for my domain controllers, another for a
specific SQL Always On cluster, another for a different cluster, another for one web
application, and so on. Never mix workloads in an availability set, as Azure has no
knowledge of the actual function of each VM. It is blindly distributing the VMs
between fault domains and update domains in a round-robin fashion with no
consideration of other factors.
Azure Storage
While aspects of Azure Compute have been covered, I also want to focus on other key
elements. The usage of Microsoft Azure Storage is a great benefit for virtual machines
for multiple reasons. The Hyper-V host has a virtualized storage driver that works
with a component, RDSSD, which consists of local cache, and then it communicates to
Microsoft Azure Storage (xStore), which has a number of BLOBs (Binary Large
Objects). The BLOBs are formatted as fixed VHDs and exist within specific storage
accounts. Microsoft Azure holds an infinite lease on the BLOBs that are considered
disks in the storage account, to prevent them from ever being accidentally deleted. The
fact that fixed VHD is used may cause concern, because you pay for used storage, and
you may create a 1TB VHD but initially use only a small amount of storage. The good
news is that the BLOB is sparsely stored; only blocks written to it are stored, so you
pay only for data written rather than for the total size of the VHD. This means that
you can safely always use 1TB as the size for your VHDs. Additionally, if you delete
content, TRIM is supported, which means that when data is deleted, the TRIM
command is sent to the storage subsystem on the Hyper-V host, which then marks the
blocks as no longer needed, and in Microsoft Azure Storage, the blocks are deallocated
so you stop paying for the deleted data.
Microsoft Azure Storage ensures that, at minimum, every piece of data is replicated
three times to provide protection from data loss. Asynchronous data replication is also
available to replicate the data to another datacenter, and it’s then replicated three
times at that datacenter, which is known as geo-redundant storage (GRS). Another
advantage of using Microsoft Azure Storage is that all existing tools for Microsoft
Azure Storage work without modification with the page BLOBs that contain the VHD,
making management simple.
Microsoft has a free tool available that enables easy interaction with Azure Storage,
Microsoft Azure Storage Explorer, which is available from
[http://storageexplorer.com/. Figure 12.12 shows the tool browsing the VHDS](http://storageexplorer.com/. Figure 12.12 shows the tool browsing the VHDS)
container, which shows the various page BLOBs used to store the VHD files that are
used by virtual machines. The tool also enables the copying of storage in addition to
downloading and uploading data.