Over Thanksgiving I was able to dedicate a couple of days to development and testing of firmware revisions and some hardware revisions to get basic disk commands, DMA, and partitioning working. Currently the disk emulation is maxing out the SCSI PHY with plenty of room for growth on the SDHC bus. Future hardware revisions will likely be based on later SCSI PHY controllers which should increase speeds to match the limits of the SDHC socket on the Teensy 3.5.
The current revision hardware manages 16MB/s between the microsd card and Teensy RAM, resulting in about 7MB/s data rate when copying between partitions on the card using the firmware console. FATfs in the firmware is much slower (used to backup and restore partition images) at around 600KB/s and likely to be an improvement goal further down the line.
DMA to/from the host results in upto 1.3MB/s with the current PHY.
Emulation of SCSI Ethernet adapters has been prototyped out in the current firmware, needing the attachment of a SPI interface ethernet controller without a TCP/IP stack. Optical drive emulation will be added in the future.