2940UW card with mix of Ultra, Ultra/Wide, Fast-SCSI2, Fast/Wide, and a CDROM

[BCinSC]

I have a pair of Seagate Ultra/Wide 9GBs and a pair of Fast/Wide 2GBs on the 68pin cable. I have a Ultra 2GB, a Fast 2GB, a Fast 4GB, and a NEC CDROM on the 50pin cable. Is having this combination of devices forcing them all to run at the least common denominator, which would be the CDROM at SCSI-1 = 5MB/sec?

 

[cardiac]

No, but your Seagate Ultra/Wide is only running as fast as your Fast/Wide 2gb drives are. Each device only runs as fast as the slowest drive on it's cable. See if you can put the Fast/Wide drives elsewhere.....

Bob

 

[BCinSC]

Come to think of it, my NEC 6xi cdrom had a Fast-SCSI-2 interface, so I imagine this one does to, as it is a bit newer (relatively). So I can put a second 2940UW in and split the drives to Ultras on one card and non-ultras on the other, as long as I have enough cables, and everything should run at their max.

9UW 2W
9UW 2W
4U 4N
2U 2N
CD

 

[BCinSC]

Found this buried deep in the Adaptec site:

Q: I was told that connecting non-Ultra devices to my card would make all my devices slow down to the speed of the slowest device. If I attach my CD-ROM to the same card I?m using for my Ultra Wide hard drive, will my performance decrease?

A: No. This is a common misconception. Since SCSI is bus structured, the host adapter can communicate with only one device at a time. It will communicate with that device based on the ID (for priority) and the BIOS settings for transfer speed. The transfer speed setting is the maximum speed the adapter will use for I/O with that device. When doing I/O with any SCSI device on the bus, the adapter will do transfer at "up to? the setting in the BIOS. Most operating systems are single tasking and will support one application at a time. If the application calls for a copy operation, for example, from a CD-ROM to a hard drive, the system will access the CD-ROM at it?s speed, download the data to memory, then access the hard drive and transfer the data to the hard drive at it?s sustained rate. Each device will operate at it?s sustained rate until the entire I/O operation is completed.