C.H.Ling wrote:
> 5x! Did you ever made a real comparison? I got 22MB per second for USB and I
> can't get over 30MB with SATA to SATA (two hard disks inside the same PC). I
> believe the HD sustain rate and other overheads in the computer limited the
> data rate a lot.
>
I have not done any careful comparisons, as a big difference was readily
apparent just watching the progress of a copy operation. I've now done a
very simple one. I've compared only read speeds for small pieces of data
- for the simple reason that my free version of HDTune only does that. I
think the results are instructive.
<http://www.moosemystic.net/Gallery/tech/Misc/WDC1500_eSATAvsUSB2.jpg>
Unfortunately, the program also rescales the graph height, so you need
to look at the vertical scale and/or the numbers on the right. Both
tests are of the same drive in the same docking station. The top one is
eSATA. It shows the typical shape, flat at first, then tapering down as
latency becomes greater as the circumference of the tracks increases
farther out on the platters. In fact, it's a better than average plot,
with a long high speed section. As it does slope down slightly right
from the start, I believe the limitation is the disk itself, not the
connections.
The second plot is of the same equipment, but using the USB 2.0 HSE
connection. The dead flat plot is a clear indication that the USB
connection is the limiting factor in speed. So at least for read speed,
the 5x raw spec is optimistic for this drive. On the other hand,
85.4/27.2 is still 3x. To date, I've only filled part of the 1.5Tb
drive, so I am still seeing something like the 90 MB/sec part of the curve.
But again, the limitation is the drive, not the eSATA connection, so
this test doesn't say what that might be capable of.
C.H.Ling wrote:
> So when we are talking about external drives for backup, then writing time is
> also very important, eSATA does not has that much advantage here.
I assume you meant to say "writing time is also *not* very important".
Sure, but the price difference between USB only and USB & eSATA was only
$US5. So why not go with the faster interface? The docking station can
handle any 3.5" or 2.5" SATA drive. The possibilities for other tasks,
where speed could make a difference, are there.
C.H.Ling wrote:
> My experience is if you have a large set of files to copy the result is quite
> accurate (did many tests in the pass twenty years), I bet no more than 20%
> variation in most cases unless your dirve is almost full.
I've never measured that. Frankly, I doubt is I will. It's obvious to me
from experience that eSATA is much faster. Just how much I don't need to
quantify.
As Chuck said, such a test is only valid if all drives are defragmented
before testing.
> To gain more speed you better go with a 10000rpm drive or a RAID setup.
That is much more expensive than a simple eSATA appliance. And the
higher speed drives don't come in the largest sizes, at least that I've
seen.
Another other factor to consider is that the 1TB and larger drives use
vertical recording, so the bit density is higher and any given read
speed can generate a higher output speed. The drive I tested has that
advantage. So I added a test of a WD 500GB drive without vertical
recording to the example. This is an internal drive, directly connected
to the MB SATA header.
As you can see, the graph starts much lower and drops much faster than
the 1TB drive. So it appears that the advantage of eSATA may be greater
for 1TB and larger drives.
Moose
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