Slow transfer speed from external HDD

I am copying a large file (18.2Gb) from a Seagate Freeagent GoFlex drive using the eSATA cable (not USB), for whatever reason when copying this file specifically it is copying at a ridiculously slow speed, about 7.17Mb/s (see attached image).

I copied a 45Mb file from it in a few seconds using the same cable. I've also copied other files of several hundred Mb back and forth getting write speeds of 150-250Mb/s, created a rar file on the drive containing two big files which I'd written to it tonight which was just over 1.5Gb, this wrote back to my Internal HDD at about 700Mb/s, so I can't quite figure out why it went so slow with that one file.

And before you turn round and say it's because of the file name length, another install of Windows created the files and directory structure and I'm just copying the whole directory structure to one of my internal drives so the directory and file name length is the same on both drives.

My System specs are as follows:

Gigabyte GA-P55A-UD6
Intel i7-860
16Gb 1600MHz Corsair RAM
MSI N470GTX
Samsung 840 Pro 256Gb with Win 7 Ultimate 64bit
WD Black 2Tb for Data (and User Profiles)
Two WD Green 2Tb drives for other Data.

Hi there

It could be the chains of the file are all over the disc rather than in a contiguous piece. I assume that the external HDD is POWERED sufficiently (especially if the file needs a lot of disk head movement to access the pieces of the file).

I'm not sure though that the data transfer speeds that windows explorer / file explorer shows are particularly accurate and they should average out in the end.

Cheers
jimbo