I have a Hitachi Deskstar 1TB 3.5" SATAII 7200rpm 16MB in a argosy HV359T external HDD enclosure.

It started having trouble transfering files (I/O errors) after a poweroutage while it was recording/writing.

I was suggested by the HDD support to do a Low Level format, which I did using the HDD Low level format tools from this site.

It is running very slowly, 40GB over 3 hours with multiple error (e.g. "Format Error occured at offset 43,531,108,352).

My questions are:
1) Can this low level format be stopped before it is done? is it a good idea to do so?
2) Should I have used the drive fitness test? Can I use it after LLF tool is done?
3) What do the "Format Error" mean exactly? physical damage?
4) what is the prognosis of this drive?

Thank you for your help in answering my questions!

I would let it run all the way through. I haven’t used the LLF tool from this site yet, had no reason to attempt a severe format.

I think it's formatting ALL the blocks, which includes bad blocks from your G-List (anyone? am I wrong? I may be) many of which are known to be bad. Otherwise I think your just running into errors with the drive reading consistently for whatever reason.

To test the consistency of the drives reading and writing, do several scans with MHDD after the format is complete and compare the results.

If the results are always the same, you can run a scan with distructive slow errase switch set and it should find any slow blocks and exclude them.

Let us know how it goes, is the format finished?