Another factor is the average files size
The smallest they are the longer will be the time required to open/close the files in relation to the copy speed.
E.G. We are copying the content of an HP MSA 60 S.A.N. from Genreral Electric Healthcare Systems, composed of 12 drives 1TB each in RAID 6 with 2 missing drives (here it come in the game, partially, the calculation needed for the Q) we have reconstructed past week. Luckily it was filled with "only" 6TB of data, but those medical images are sets made of the image + a small set of description files.
This drops the copy speed to an Average of 4MB/sec
This turns in 330/360 GB/day
Which will end in a copy period time of something less of 20 days
UPS for everything and crossed fingers