Hard drives by themselves don't really confirm the files have been copied... but most PSDs have some mechanism to test file transfers... often the most simple approach is to verify that file name and file size after the transfer is done, etc... beyond that, it takes more effort and time... The NextoDI products have a interesting feature that doesn't seem to be on any other PSDs... if you insert a card that's already been copied to it, it will tell you that it has a copy of the card already. You can then do further verification or copy the card again if you choose to.
But anyway... you should at least be aware... that even a full bit by bit comparison of the data on the HDD to the data on the flash memory card is not necessasarly going to tell you that the data is not corrupt... If the device is reading the memory card incorrectly, it's possible to copy the bad data onto the HDD and then when you compare the two it passes the comparison... but still the data is not correct because it isn't being read correctly from the card... So, while some PSD's do full bit by bit comparisons... it's really not fool proof...
On the other hand... it's really quite rare for a good PSD to incorrectly copy the data... I've never had data corruption caused by any production PSD that I've used. I do beta testing, and I've seen it happen in beta versions of a product, but never in a production product. Not to say it can't happen... just that it really is kinda rare....
I did have data corruption caused by a bad flash card... but it was the case that verification really would not have caught the problem...
Some devices can write back to memory card... a poor man's viewing PSD is to copy the data to the PSD, then write it back to a memory card, put the memory card back in the camera and use the camera to view the photos... this can give you some since that things are working correctly... even this is not fool proof howerver, since some cameras do not really decode RAW data, but rather display a smaller JPEG version of the file... (some viewing PSDs do the same thing)
Thanks to you both.
Your thoughts are very helpful.
Still, a couple of more questions:
Do the hard drives confirm that the files have been copied correctly?
Just how bad is the viewing screen on the Wolverine and Archos,
e.g. how does it compare to photoshop slide show before the view is
rendered (i.e. just identifiable but you know the file is
readable). I could live with viewing only JPG's as seeing them
would likely mean the RAW file was OK. Is there any limit on the
size of the JPG's.
In Canada, the Epson is now about $850. The Wolvserine and Archos
are between $400 and $650 so the cost difference is substantial if
all are equally reliable. We are planning on travelling to Greece,
will need about 4G a day of storeage and would hate to lose all our
photos.
Thanks again.