I have noticed that the slowest drive in my system is used most during an msi installation. I mainly notice this when running windows updates but it seems to be msi installs in general.
The setup I last saw this occur on was running Windows 7 with the following drives:
240GB SSD NTFS ~515MB/s Operating system drive
1TB NTFS ~110MB/s
4TB ExFAT ~80MB/s
I would think that windows would choose the fastest drive with available space for temporary files. But it will instead choose the external drive with the slowest transfer speed. I could also understand choosing the 1TB for not being an ssd in an attempt to preserve the longevity of the ssd write capacity. Why does this happen? Is there a way to force these installations to use the OS drive or a specific drive?