Consistent failures on backing up to external USB drive

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OS: 10.4.6

System: Dual G5/2.0GHz/4Gb RAM

Retrospect 6.1.126 / driver access 1.0.107 / driver update 6.1.7.101

 

I've recently installed a 320 Gb SATA drive into a SATA/PATA external case accessed via USB (the case supports USB 2.0).

 

Backups using Retrospect consistently report 'miscompare at data offset' and other errors (e.g. checksum errors, etc.).

 

Backing up the exact same data to a different external Firewire drive on the same machine works just fine; no errors at all.

 

This suggests one of these might be at fault:

- Retrospect doesn't like USB on 10.4.6

- 10.4.6 doesn't "play fair" with USB drives

- the brand-new Seagate drive is effectively DOA

- the external USB <-> SATA case is somehow faulty

 

I've tried using different USB ports on the machine, its not the particular port. I've tried jumpering the drives from 3Gbps to 1.5Gbps; no difference (in any event in either case, the transmission speed is limited to 480Mbps according to System Profiler).

 

Any suggestions are welcome. Is anyone experiencing trouble with using Retrospect to external HDs over USB? I'm considering upgrading to OS 10.4.7 but I get reports of more trouble with external drives on 10.4.7, so... what do people here think?

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Forgot to add, I'm doing a 'File' backup. The backup is big, 150Gb+. I haven't yet tried using a "Removable Disk" backup, which is another thing to explore; I can't imagine it'd make a difference, though.

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Not exactly a high-volume forum!! ;-)

 

More seriously, upgrading to OS X 10.4.7 seems to have cleared this problem. Strictly speaking I may be speaking too soon as I need to do more testing but at least for the first time a decent sized backup as gone through with a a few hundred-odd error messages. For those who do have external USB devices, it would seem that you might have to avoid OS X 10.4.6 -- ?