If you use external firewire disks with your PC, you may have seen at one time or another the dreaded “Delayed Write Failure”. Why does this happen?
Apparently, it’s because various Firewire enclosures have problems supporting more than 128 KB in a single transfer. Depending on the Windows application software, this may or may not cause problems for you.
There is a convenient Filter driver that overcomes this problem, by telling Windows to limit transfers for a particular device to 128 KB; you can find it on the Max 128K Filter Page.
That same page also references another very useful resource, the busTRACE free utilities page. This includes a utility called 1394test which will show you whether your Firewire enclosure suffers from this problem or not, as well as other useful related utilities. The 1394test page also includes extended discussion of the whole Delayed Write issue.
Note: apparently Windows XP Service Pack 2 also includes code to limit the maximum transfer size to 128 KB — so if you are running Service Pack 2, you may not have the problem at all.
(Thanks to Steve for pointing me towards these.)