This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
DMA needs to be turned off with the Apple HS SCSI card or the RamFAST revision C card. It does not need to be turned off with the RamFAST revision D card (differentiated by being half sized). Current RamFAST cards are revision D as are late model CV Tech cards. It is the RamFAST revision D that is designed to DMA into any RAM card, even 8MB models. It was made around the time of the CV RAM 8MB model that turned into the RAM GS Plus, but functions just as well with the Sirius card. By: Scott G