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We have 11 client Sites hosted on Azure PAAS setup with SQL on standard S2 tier. We also have planned to remove Inrole cache and Implement SQLSession Cache on these Production servers.

For all 11 sites , we expect 300-500 concurrent users per site. Is there any formula to calculate if the S2 tier is sufficient for this user load.

Also , is there any documentation on the Max concurrent workers/Max concurrent sessions for Sitecore 8.0, this information would help us understand if the S2 tier will be sufficient for the given user load.

Azure documentation for S2 plan

Max concurrent workers - 120

Max concurrent sessions - 1200

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There's no formula, because the workload is as much a function of your code as it is about the number of concurrent users. If you are using caching properly an S will be sufficient for "web" but not "master". If you have a logged-in area you will load up "core" as well.

My suggestion is to start with S3 for master and web, and monitor the DTU, CPU, IO and connection telemetry during peak operation, and during publishing. There's graphs in the portal.

If you rarely hit 60-70% then turn it down to S2. There's a big drop to S1 stop don't be tempted by that. Remember you can change these scales in about an hour with virtually no disruption to traffic. Write a powershell script and run it on a timer to scale up/down at 2am or whenever your site is quiet.

EDIT: Forgot to mention that at the moment all our deployments are done with SQL Elastic Pools instead of individual databases. This has the advantage that you can 'thinly provision' resources to the environment, knowing that while individual databases require burst capacity, they don't all need it at the same time.

Our current starting setup is a Standard 100 eDTU pool for non-production (including Core/Master/Web/Analytics) and Premium 125 eDTU pool for production.

I'm still on the fence on whether a P125 is better than a S200 for 40% extra cost, but 35% less eDTU. We're still evaluating that. The main difference is that with the Standard pool each individual DB is capped to 100 eDTU, which is not the case on the Premium tier.

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I had the same question when started to deploy a client using Azure SQL and I couldn't find any formula to guide me the number of max concurrent workers and sessions.

I've also wrote a blog post sharing my experience using Azure SQL, and at that time Sitecore recommendation said:

"It is recommended to use at least the Standard S3 Azure SQL tier on any production systems"

So, in production environment please go forward since beginning with Standard S3 tier.

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