All I can say is on a busy server any SQL install, but especially a cluster install, can take a long time.
The SQL cluster install process does a lot of disk status checking, and fast execution time depends on fast IO to the disks. I do not know what process is used internally, but the performance profile makes me think Server Message Block calls (eg Named Pipes) may be used in some of the processes - SMB tends to add to any delays that might be encountered and is possibly why SMB was totally rewritten for Windows 2012.
Anyhow, for example I have found when testing SQL FineBuild that running a single SQL install where all files are targeted to a single physical disk may take 1 hour, running two simultaneously to the same physical disk may take 3 hours for them to complete, and running 3 simultaneously may take 6 hours to complete. If I run the same installs simultaneously but targeted at separate physical disks, then they all finish after maybe 1 hour 30 minutes. My desktop-based test environment does not reflect what an enterprise-quality server will do, but it does show that SQL install times can significantly increase if the server has a IO load.
Original author: https://github.com/SQL-FineBuild/Common/wiki/ 1-click install and best practice configuration of SQL Server 2019, 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005.
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