Poor SCSI performance in OSX vs OS 9


I am using a magneto optical drive to view images for a healthcare business.

The time to load images in the program via a 400mhz g4 OS 9 = 40 seconds and the time on an 800mhz g4 with OS X is somewhere around 60-70 seconds.

The MO drive is SCSI.

Does anyone have any ideas as to why this would be? Is there known issues with SCSI drivers in OSX, etc?


Is this a Iomega MO 1.3Gb?
Is it 25 or 50 pin SCSI?

From what I understand MO drives generally used an Ultra SCSI interface with high-density 50-pin connector. This interface is capable of transferring data at up to 20Mb per second, but the Iomega 1.3Gb magneto-optical drive mechanism is limited to a lower rate of about 6Mb per second.

It seems to me that you haven't configured the 800mhz G4 (mac OS X) properly and as a result it is reverting to standard SCSI - about 1.3MB/sec (instead of Ultra SCSI).

Seeing as no G4 came with in-built SCSI - I'm assuming that you are using a PCI SCSI card. Is this an ATTO or Adaptec card? I'm also assuming that you are using the same PCI card in both the 400mhz and 800mhz Mac's. If that is correct - you can be pretty sure that the problem is SCSI driver related.

I don't imagine that you would notice too much difference between the 400mhz and 800mhz G4 processor speed - as your main bottleneck is going to be the 6Mb MO SCSI interface.

Since OS X arrived - SCSI on a Mac has been in sharp decline - and as a consequence has suffered from decent support and new drivers. I have personally found that depending on which OS X you are running there is a specific SCSI driver for each OS version. OS X usually comes with these drivers installed into the basic install - but you need to check... And often there are updated drivers available.

Go to the relevant SCSI card's manufacturers website and download the most appropriate driver for your version of Mac OS X.


It is a Sony MO drive, don't have the specifics on the pins and such at the second, but the specific drive is Sony SMO-F551-SD

Let me know if that helps anything...


Classic mode runs a LOT slower. But it is acting like its reading at 1.3mb/s (61 seconds for 92 mb file). Perhaps it is supposed to be ultra scsi?

The weird thing is, when reading a second time, it loads completely from memory, doesn't access the MO at all. None of the other machines (that read faster) do this. It seems the reason it is taking so long is it is taking from the MO, storing to memory, and when finished, then reading from memory the data. Is there any way to change the memory handling?