View Full Version : Mixing ultrawide and LVD drives on the Adaptec 2940U2B

03-20-2001, 01:18 PM
Mixing ultrawide and LVD drives on the Adaptec 2940U2B

Can anyone help me through the SCSI forest to decide whether the Adaptec Adaptec 2940U2B would be useful in my situation?

Computer = Beige Minitower G3/333 that came stock with Apple (ATTO) ultrawide card and 9 GB Quantum drive. Currently, the SCSI controller is an ATTO Express PCIPro PSC, a Single Ended Ultra-Wide card that ATTO said was an exact replacement for the Apple ATTO card, which failed last year. I was warned that this card and the ultrawide bus cannot function reliably with more than 4 devices or a total cable length of more than 1.5 meters. Even though the card has an external 68 pin connector, I was told not to use it or I would exceed the bus capacity.

Internal Drive #1 (stock) = Quantum Viking II 9.1 WSE Version 4110
Internal Drive #2 = Seagate 9GB ST39140W

These 68 pin drives and the ATTO Express PCIPro PSC are working fine, with transfer rates of about 13 MB/sec

My overall goal is to add external devices to the 68 pin bus. Currently I have 6 external drives, all appropriately jumpered to run off the narrow SCSI external bus (which reduces their speed to about 4 MB/sec). Some of these drives are capable of much higher speeds:

External Drives #1-4 = Quantum Atlas IV LVD 36 GB QM336400KNLW
External Drive #5 = Seagate Cheetah 9 GB 18LP ST39103LC
External Drive #6 = IBM Ultrastar 18ES 9 GB DNES309170W

For security reasons, I need to have any two of my four 9GB drives internal, and all 4 of the 36GB drives and the remaining two 9 GB drives mounted in external cases. My questions are:

1) If I l buy the 2940U2B and leave the Quantum Viking II 9.1 WSE and the Seagate 9GB ST39140W as the two internal drives, and add the four Quantum Atlas IV LVD drives to the external connector of this card, will the card be able to negotiate between the 2 ultrawide and 4 LVD drives to achieve the maximum speed of each, or (as I fear will occur), will the speed be limited to the slowest drive on the bus? This would not be intolerable, if it would be faster than the 4MB/sec I can achieve now. Or would this mix of ultrawides and LVD drives be unstable?

2) If I switched external drives 5 and 6 to be the internals, would this help achieve the faster speeds? The Cheetah (#5) is an LVD 80 pin, adapted down to 50 and 68 pins. However, I believe the Ultrastar (#6) is only an ultrawide, similar to the two existing internal drives, so it would not provide a benefit, correct?

3) Is there an alternative SCSI card that would still be inexpensive and achieve my goal of getting more speed out of the 4 Quantum LVD drives?

Sorry this is so complex. Any advice will be appreciated, but I cannot buy more drives or a $400 two-channel card - I am at the end of my budget.



03-20-2001, 10:47 PM
the fundamental rule (http://www.macgurus.com/graphics/mgwhichscsiadapters5.html) applies: do not mix single-ended and LVD devices.

since it is not advisable to use more than one SCSI board in the beige G3, it seems you are faced with a decision: to live with the limitations imposed by single-ended ultra wide cabling, or migrate to LVD. If you migrate to LVD, and use only LVD drives on an LVD bus, with appropriate LVD cabling and termination, you will indeed find that the 2940U2B will be useful.