The first Sun3 servers weren't equipped with SCSI disks. In these days SMD disk were state of the art. Sun used the Xylogics 451 which sat on a Multibus-VME-Bus adapter. This beast (brand ttl grave) was dumb and slow. Later sun sold the Xylogics 753 (or 7053), which is much better.
People who needed fast disks early in 1986 had to look for third party disk controllers. Ciprico made the Rimfire 3200 which could serve four SMD drives and later the 3400 which could serve four ESDI disks.
The Rimfire does have 512 kB cache, can use DMA and all I/O operations are done via shared memory. This makes it much faster than the Xylogics 451 and even the Xylogics 7053 isn't any faster.
To be able to boot from the Rimfire the machine needs special boot ROMs. Later versions had an Xylogics XY451 emulation so they didn't need such tricks. But these Rimfire make more trouble when used with the rf driver.
I've packed all software (drivers, format-utility, boot sectors) and Usenet artices together that i have for the Rimfire and made it available for download here.