Is there a way to fake "slow" storage for testing?

Solution 1:

If you run your software in a virtual machine, using Windows Server 2012R2 as a hypervisor, you can set storage QOS on each disk, limiting the throughput to the IOPS you want.

Solution 2:

I'm not familiar with any products that will do this for SATA or SAS. For that you'll need to introduce a real load and performance test.

If you are referring to network storage there are a number of options.

I generally whip up a set of VMs, one of which is set up a transparent network bridge. I prefer CentOS but that's just my background.

By using the TC / EM packages you can emulate a slow network, therefore slow NAS, iSCSI SAN or SMB response. I've done so on several occasions.