We recently moved our websites from IIS 7.5 to IIS 8.5.

  • We did not change any of the code in the websites
  • The app pools are identical in configuration
  • We are running ~70 sites on this server
  • The old server had 6 gig of ram, dual 2.4 GHz processor
  • The new server has 12 gig of ram and a 3 Core 2.4 GHz processor
  • Both the old and new servers are:
    1. VM's
    2. Using app fabric for session state
    3. 64 bit
    4. Have the same versions of .NET installed (4.5.2)

On our old server we never experienced memory issues.

The new server started at 6 gig of ram and was getting out of memory exceptions. We kept bumping it up until the server became more stable.

On our old server we would normally see 70-75% RAM utilization.

On the new server we normally see 98-99% RAM utilization, this is regardless of the RAM on the server.

The app pools in general are using 2-3 times the amount of memory they were on our previous server.

For example, we have one application pool that was consistently running at 350-400 meg of ram on the old server. On the new server the same pool runs at 800 meg - 1.2 gig.

We have scoured google, serverfault and stackoverflow to see if anyone else has experienced a similar situation to no avail and help would be greatly appreciated.

  • What we ended up doing to solve the issue was to move the application pools from a 64 bit pools into 32 bit pools. This stabilized the memory consumption and it returned to expected levels. – Terry Anderson Dec 23 '15 at 16:25

We had the same symptoms during a transition from Server 2008 R2 and IIS 7.5 to Server 2012 R2 and IIS 8.5. Turns out in our situation it was a missed setting on new configuration in .NET Framework config. Needed to set the performance scenario to HighDensityWebHosting (http://www.asp.net/aspnet/overview/aspnet-and-visual-studio-2012/whats-new#_Toc_perf_5)

We had set this but in haste accidentally made it in the 32bit framework (Windows\Microsoft.NET\Framework\v4.0.30319\aspnet.config) instead of the 64bit settings (Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet.config). Ugh.

After getting correct settings we are actually seeing app pools for our application use about 1/3 less RAM on IIS 8.5 vs 7.5

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