I have a brand new external hard drive (the Lacie Porsche p9230.) Why do all my attempts to do a time machine backup stall? (usually immediately)

I have a brand new 3T external hard drive (the Lacie Porsche p9230.) I manually backed up several big files from my computer ok, but all attempts to do a time machine backup just stall, usually after only a few K are backed up. hours go by, no progress.

The first time, it did 3 gigs in just a couple minutes, it then got to about 9 gigs, then nothing for 2 hours. all subsequent attempts have done merely a few k, or megabytes, then all just stopped, still appearing as if they are proceeding, but with no results over a long time.

It could indeed be the hard drive on my computer itself, but aside from this the computer functions normally, though slow (it's old, 2009.)

As stated. I WAS able to manually back up a folder exceeding 250 gigs in size, and then another of about 14 gigs.

So, why can I nt do a time machine backup, effectively?