Post by firstname.lastname@example.org
I have an external hard drive connected to USB2 port on 64-bit W7 Home
Premium. I use it to make backup copies of my data using windows
My data is in a separate folder called coincidentally My_Data.
I initiated a copy/paste from My_Data on the W7 drive to a same-name
folder on the external drive. I see the transfer is said to be
8MB/sec. Then I initiated a second copy/paste of my three 'desktop',
'downloads' and 'documents' folders on the W7 drive to same-named
folders on the same external drive. The transfer is said to be
Why the different speeds? I certainly would prefer the faster speed.
As it is, the slower transfer will take more than a day to complete.
The seek time of any hard drive involved in the transfer
is not zero. Imagine 1KB files which are spread all over
the platter surfaces. If it takes 12 milliseconds for the heads to
move to the other part of the disk, you can only transfer
80 files per second. If each file is 1KB in size, your
transfer rate is 80KB per second. It's not unusual to
see 1MB/sec transfer rates, when the files are small and
If you reduce the number of seeks, and increase the
size of each individual file (to encourage sequential
reads or writes on the hard drive), then the performance
should pick up. If you were transferring four DVD-sized
ISO files to the external drive, that would happen
at 30MB/sec. Because there might only be four large
head movements, while the rest of the time, the
transfer was purely sequential.
If all the files in question, were stored in a single 7ZIP
file (7-zip.org), then the ZIP file would copy over at
30MB/sec. But of course, the mere act of making a ZIP
of the scattered files, also invokes the 12 millisecond
hard drive seek time, so as a practical matter, the
idea has no merit. It would take far longer to make the
ZIP than time saved during the transfer.
Note that, even if both the source drive and the destination
drive were SSD based, the transfer would still be a little
bit slow. The file system has an upper limit on how many
files it can process per second (maybe 5000 to 10000 files,
when the IOP rate of the SSD could be 100,000 to 200,000).
And this is why technologies like NVMe are kinda pointless
at times, because the file system performance has not scaled
at the same rate as the Flash storage is speeding up.
You can get USB3 cards for both PCI slot and PCI Express slot.
Because the PCI version costs twice as much, and the designs
aren't kept on the market due to poor sales, there's no guarantee
on a given day that you can find one for sale.
PCI USB3 - 100MB/sec (bus limited, board uses bridge chip and USB3 chip)
PCI Express Rev.1.1 USB3 - approx. 200MB/sec, bus limited.
PCI Express Rev.2 USB3 - approx. 400MB/sec, bus limited.
Southbridge USB3 - maybe 450 to 500MB/sec via UASP protocol
The best USB3 is the port on a Southbridge, and this is due
to the roughly x4 lanes of transfer bandwidth in the chipset,
rather than some "design genius" in the block itself. It's
because the PCI Express versions don't have a wide enough
So even if you have an older computer, with only PCI
slots, you can still get better speed. You would need
a new enclosure for the external disk, with its own USB3
peripheral chip, to get that speed. I got a couple USB3
enclosures here for around $35, but they top out at around
200MB/sec. Which means, "they're good enough" :-)
When a 200MB/sec enclosure is plugged into a 500MB/sec port,
you only get 200MB/sec, and only on sequential transfer.
If I repeat your "small file" exercise, I can expect 1MB/sec
even with the faster port.
So it *still* doesn't solve the small file problem. But it
does help when you want to do a full backup of C: .
When Macrium Reflect Free or other VSS based backup programs
make backups, they use sequential transfer techniques. So the
head *doesn't* fly all over the disk during the backup. And
the rate can be much higher as a result. The software makes
a map of what clusters need to be transferred first, so it
can plan the least disruptive head movements on the disk.
In some rare circumstances, it may be faster to transfer the
whole partition, simply because of the reduction in head
But if your rate is 8MB/sec and the best case is 30MB/sec
on the destination device, there isn't enough elbow room there
to make it worthwhile fiddling with the transfer. Just do it,
and wait the whole day or whatever. Many times I try novel
transfer methods, only to realize later that I wasted more
time setting up the novel method, than I could ever save in
practice. If I had a 100-200MB/sec pathway to destination
storage, then I might use Macrium and just back up the
entire partition. It depends on how "miserably small" the
materials are that need to be backed up, whether I
would resort to such a technique.