To use the PiSCSI interface, simply enable it by uncommenting the setvar piscsi line in default.cfg, or add it to the config file you're currently using.

Add disk images to the PiSCSI interface by uncommenting the piscsi0 and piscsi1 lines and editing them to point at the disk image(s) you want to use.

Physical drives can also be mounted using their mount point files on Linux, such as /dev/sda for a USB stick, but keep in mind that this is dangerous as it can destroy the contents of the disk.

You can mount up to 7 disk images using setvar piscsi0 through piscsi6.

If you want EVEN MORE speed, either adjust the size of your hard drive image so that it gets properly detected with 16 heads in HDToolBox or manually edit the Cylinders/Heads settings when setting up your drive.

(The trackdisk device on the Amiga seems to enable transfers bigger than 512 bytes (one sector) only if the drive is identified as having more than one drive head/surface.)

Making changes to the driver

If you make changes to the driver, you can always test these on the Amiga as a regular file in DEVS:, but the Z2 device has to be disabled for this to work properly.

Steps to create an updated boot ROM, all of these are done in the device_driver_amiga directory:

(Optional) If you've made changes to bootrom.s, first run ./build.sh.
(Optional) If you've had build.sh create a new bootrom file, you need to chop off the first few bytes of it, since VASM adds a single hunk to the beginning of it. Simply delete all bytes up until you bump into the value 0x90, this is the first value in the boot ROM identifier.
Compile the new pi-scsi.device using ./build2.sh.
(Optional) If you haven't previously compiled the makerom binary, or the code for it has been updated since last time, simply run gcc makerom.c -o makerom
Run ./makerom to assemble the boot ROM file, it's automatically in the correct place for the emulator to find it.

If you for instance want to mount a FAT32 disk with fat95, these old instructions may be of some use:

Download giggledisk from http://www.geit.de/eng_giggledisk.html or https://aminet.net/package/disk/misc/giggledisk to make MountLists for attached devices. Place the giggledisk binary in C: or something so that it's available in the search path.
It might be a good idea to have fat95 installed on your Amiga, in case you want to use FAT32 images or other file systems that fat95 can handle: https://aminet.net/package/disk/misc/fat95

Now open a new CLI, and type something like: giggledisk device=pi-scsi.device unit=0 to=RAM:PI0

This will create a MountList file called PI0 on the RAM disk, which contains almost all the information needed to mount the drive and its partitions in Workbench.

You'll have to start up your favorite (or least hated) text editor and change the contents of the file a bit.

Above the FileSystem line, you'll notice a drive identifier. This line might say something along the lines of DH0 or PDH0, etc, and it must be removed, otherwise the file can't be parsed.

The FileSystem line will usually be empty, so you have to fill this out yourself. For instance, you can set it to something like L:FastFileSystem to use the standard file system for the drive, or L:fat95 in case the image is in a format that fat95 can handle.

Thus, an edited line would look something like FileSystem = L:FastFileSystem

If the MountList has several partitions listed in it, it must be split up into separate files for all partitions to be mounted.

Once you've edited a MountList file, simply copy/move it to SYS:Devs/DOSDrivers, and the drive will be mounted automatically the next time you boot into Workbench.

If you don't want it to be mounted automatically, simply use the Mount command from CLI.

A big word of caution

While the PiSCSI interface can be used to mount physical drives that are available as block device nodes on the Pi, you should not do this unless you are absolutely sure what you're doing.

Directly mounting a block device connected to the Pi may corrupt or destroy the data on the device, depending on what you or the file system drivers do with this disk on the Amiga side.