What is the main difference between “Extra Large and A5 instances” in Azure? I can see that there is a difference in CPU cores and also a mention that you must use A5 for “memory” intensive operations. I understand memory intensive as a word, but why would IIS be hosted in 2 cores (A5) when there is a choice for 8 cores (Extra Large) (with the same 14 GB RAM)?
The MSDN page Virtual Machine and Cloud Service Sizes for Windows Azure perhaps makes this more clear.
You can see from the table that in all aspects (CPU, disk, IOPS, etc.) the A5 instance is sized identically to the Medium instance, except that it has four times as much RAM. The same for A6 versus Large, and A7 versus Extra Large.
You would use such an instance if your application is truly memory-intensive, and needs fewer of other resources such as CPU and disk in relation to memory. Whether that is true of your application is something you will have to figure out for yourself.
In my experience it’s not typical of web sites to be memory bound; they usually are CPU or I/O bound. I would not consider a memory intensive VM unless I knew the web app needed far more memory than is typical of a web site.
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