I don't think the A2090 can be expanded beyond 4GB (missing SCSI direct commands and updated drivers) - if it all. There might be as small a limit as 512 MB; BBoAH states that partition size is limited to 256 MB.
I've long ago stowed away my A2090A as it's a major pain in the *ss to set up and would rather go for another / better SCSI adapter.
