File Transfer to External HDD via USB very slow. What may be the problem?

Hi all,

I was transferring some files from my iMAC hard disk to my external HDD (USB) but the transfer of one particular file (around 900MB) suddenly went very slow! It took around 10 minutes to complete that transfer! My cursor turned into the color wheel for a few seconds before that transfer started and from there, it took around 10 minutes to complete.
Once the transfer was completed, I moved that file to trash and emptied the latter.

Can anyone point out what the problem might be?

regards,
Ali
(Mac OSX 10.7.5; 8GB DDR, 500GB Sata HDD)

USB 2 is slow - fact of life - the larger a single file happens to be, the slower it is going to transfer.
Try moving a 4 GB + single file via USB 2 - omg.

Pinpointing the cause of a one time occurrence on a computer is like finding a needle in a haystack and a pointless waste of time.

Thank you for your response bobtomay!

I understand file transfer of large files via USB can be slow. I have transferred files of the same size and larger sizes on that same external HDD and it went faster!

After some more research, I've found that bad sectors on either disk may be one of the causes of slow file transfer.

bad sectors on the disk, the file itself is corrupted, either one of the drives was busy reading &/or writing other data - like if you had a browser open while transferring, all sorts of stuff.