My laptop is a Dell XPS 13 9360. I was pleased with it when it arrived in September 2017, and still am. Six years ago, I thought its 220 GB SSD would be plenty. Now, despite the cloud, that drive was often almost full, in part tested by Haskell’s requirements. I turned to an external SSD, a ‘1 TB’ (actually, 1012 B or 931 GB) Crucial X9 Pro, for about £ 70.
exFAT v NTFS
The drive came formatted as exFAT, supported by Windows and macOS. I discovered that exFAT does not support symbolic links. So, I reformatted the drive as NTFS. NTFS is not fully supported out of the box by macOS.
Drive letter
Windows assigns drive letters after C as they are needed. However, I assumed that, in practice, the external drive would be assigned letter D.
Speed
The drive was marketed as having a speed of 1,050 MB/s (maximum sequential performance). Commanding winsat disk -drive D yielded ‘disk sequential 64.0` 730.97 MB/s (read) and 693.60 MB/s (write).
The Haskell Tool Stack
The Stack root directory is determined by environment variable STACK_ROOT. I set it to D:\sr.
On Windows, the Stack programs directory is determinated by the local-programs-path configuration key. I set it to D:\sr\programs. This caused Stack 2.11.1 to fail to install MSYS2, because the drive differed from that of the system temporary directory. This will be fixed in Stack 2.13.1.