Azure Files is an excellent service, providing file-system (SMB) based storage on the cloud. It has been very useful for us together with Azure Kubernetes Service.
Functionality-wise, I have no complaints. While there are a few things that could be better, the service overall provides good value, and the addition of Premium File Storage is definitely a very interesting and exciting option.
I have been, however, dissatisfied with the Billing experience.
Cloud Billing Transparency
I’m a strong believer that Cloud-based offerings need to have a clear set of billing rules that customers can clearly understand and use to budget their cloud costs. There are 4 key elements that I believe contribute to having clear and transparent cloud billing for usage-based services:
- The publicly available pricing information should clearly document what billing meters are used and how these relate to the prices listed.
- For services that charge for communication, any related billing meters should have a clear relation to the underlying protocol operations and semantics.
- The service should provide metrics that allow customers to understand their usage.
- Any metrics should clearly relate to the corresponding billing meters, so that the customer can audit their bills for accuracy.
A customer that understands how your service is billed, budget properly for it, and also audit the usage is a happy customer.
The Azure Files Billing Conundrum
Why am I generally unhappy about how Azure Files are billed? It’s not so much that I object to the actual cost of the service (which is generally reasonable for most scenarios), but that I believe that Azure Files breaks several of the rules above.
Let me explain why.
Pricing Information vs. Billing Meters
The first issue I have with Azure Files is how pricing information is presented. There are two separate components: Storage and Operations.
Storage pricing is very clearly presented, but Operation pricing is very deceptive.
Billing meters are only partially related to how pricing is presented. While pricing talks about “Put, Create Container Operations” or “List Operations”, billing meters include things such as “protocol operations”, and “lrs write operations”. You can guess about how they are mapped in some cases, but not all of them.
I would much rather the pricing information was presented by outlining the meters used and what each one measures exactly.
Billing and Protocols
Azure Files operation pricing is stated in terms of the underlying operations on the REST API. This is fine if you’re accessing the service over the HTTP interface, but that’s not really the common usage for Azure Files.
Instead, you’ll mostly be accessing the service over SMB from Windows or Linux machines, and so there’s
no clear relationship of how a File-System-based operation (such as Open File) maps to an operation
on the REST API. This leads to significant confusion and makes it easy to budget incorrectly for the service,
understimating the actual costs.
For example, I ran into a case where a service would often open a file, read from it, and then close it. I was pretty surprised that my Azure Files bill was primarily composed of “Write Operations”. Well, surprise-surprise, turns out that the file-system open a file operation is considered a write operation for billing purposes. There was absolutely no way for me to figure that out before I wasted a lot of time and a few support cases (which went nowhere) on it.
Meters and Metrics
Azure Files supports some basic metrics, which get stored in Azure Storage Tables on the same storage account. While these are useful in general, they are not very useful to audit your usage costs.
This is because the metrics, again, bear no direct relationship to the billing meters. For example, you will see things like this in your storage metrics:
user;Createuser;SessionSetupuser;Writeuser;GetFileuser;QueryInfo- … and more
These bear a little bit more relationship to the file-system semantics of Azure Files access over SMB (but still only partially). The big problem is that there’s no obvious way to relate the metric values to the corresponding Billing Meters being used. We can guess about what some of it means, but since it’s essentially undocumented, it does not provide a base that’s stable enough to actually audit your bill.
It also clearly doesn’t relate very clearly to the public pricing information, either.
But beyond the obvious disconnect with pricing/meters, there’s an even more annoying issue with Azure Files metrics: They don’t provide enough information to actually troubleshoot billing issues, because there are no corresponding access logs for Azure Files.
So if my Azure Files bill grows 10x in write operations, there doesn’t appear to be a way to figure out what shares, folders, or files are actually getting accessed and thus triggering the usage increase. Even Microsoft Support appears unable to obtain this information, which means that if you run into such a case, you’re stuck trying to figure things out by trial and error.
Conclusion
While Azure Files provides an excellent platform for cloud services, make sure you understand exactly what your usage patterns are and keep in mind that the file-system nature of the service seems to be very much at odds with how the pricing information is presented. Expecting some surprises in your bill while you understand your usage patterns better might be a good idea, too.
