s|b said:
Although the external hdd is USB 3.0 I think it will be slower to copy
the image directly to it. I tried it once (long time ago) on a USB 2.0
drive and it was very slow. Also, I bet on more than one horse. I'll
keep a copy on my internal drive /and/ on my external drive.
You should try a USB3 enclosure some time. They fly.
Especially if plugged into an actual USB3 connector on the computer.
USB2 hard drives, cap out at around 30MB/sec. That's what
you were seeing. USB1.1 hard drives, only manage 1MB/sec (like
on my old Macintosh). You haven't seen pathetic, until attempting
to transfer files to an older Mac.
A "good" USB3 enclosure chip, has a bandwidth of around 200MB/sec sequential,
sufficient for my new hard drives at 135MB/sec or so. The USB3 no longer
gets in the way of file transfer, like on USB2. The hard drive still
has the same seek time though (slow), and if you were copying 5000 small
files, the net transfer rate (with all that head movement), is in the
low megabytes. But if you copy a DVD movie over USB3 (one single large
file), to a hard drive, you could see that working at the full speed
the hard drive is capable of.
To give a (not very good) example, I own a USB3 32GB key. I don't
have a USB3 connector on any computer. The USB3 key transfers at
35MB/sec using USB2 protocol (somehow, it manages to do better
than the other USB2 keys I own). The device is rated for only 45MB/sec
if plugged into an actual USB3 connector. That's because that particular
key is only $20, and isn't a multichannel type. Some of the fatter
keys, can get close to 100MB/sec in the same scenario (USB3 key to
USB3 computer).
So if investing in a USB3 enclosure, you need the proper add-in card
for an older computer. To make it all work well. And since I only
own one "USB3 peripheral", I haven't bothered buying a card yet.
With a USB3 PCI Express card (two connectors on faceplate),
and a USB3 external hard drive, you should be able to get
well over 100MB/sec. It would be around 200MB/sec, if the
hard drive type used in the enclosure, was an SSD. But SSDs
aren't cost effective for doing backups - a regular hard
drive is cheaper per gigabyte of backup storage.
Paul