availability calculation of a azure service fabric stateful application
Virtual Machine Scale Sets (VMSSs) don't have a SLA of their own:


  Virtual Machine Scale Sets is a free service, therefore, it does not have a financially backed SLA itself. However, if the Virtual Machine Scale Sets includes Virtual Machines in at least 2 Fault Domains, the availability of the underlying Virtual Machines SLA for two or more instances applies. If the scale set contains a single Virtual Machine, the availability for a Single Instance Virtual Machine applies. See the Virtual Machines SLA for more details.


The above statement points to the fact that VMSSs are just an orchestration layer over the top of Virtual Machines and as you quite rightly pointed out results in an availability for a VMSS of 99.95%.

In terms of the storage calculation, there are several parameters here:


Whether you are using Hot or Cold storage, the availability for Hot storage is 10 times that of cold storage.
Whether your application is read or write heavy, what you need to consider here is that there are separate SLAs for reading and writing.


Let's make some assumptions:


Storage is, in general, cheep.  Therefore, only ever use the Hot Storage Tier.
Managed Disks are, in general, easier to use.  Therefore, you are limited to only using Locally Redundant Storage.


With the above two assumptions your storage SLA is 99.9%.

Multiplying these two figures together you get, 99.985%, this is still kind of low, but higher than your 98% figure above.  You can increase this number by hosting Service Fabric across multiple regions:



This would give you system availability close to four nines, i.e. 99.9898%