External USB case for 2.5 inch SATA drive

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I have a Western Digital WD5000BEVT 500GB 2.5" Hard Drive SATAII
5400rpm 8MB Cache - OEM Scorpio Blue hard disk.

I wish to purchase an external USB case in which to place this disk.

I am looking at Safecom products 2.5" SATA / IDE HDD
USB 2.0 Enclosure

         model SU2-25SJA


     and model SU2B-25SPJA


The former says it supports hard disks of capacity up to 320 GB
and the latter of capacity of up to 160 GB.

What is it which places a limit on the capacity of the disk
which can be used with these enclosures, and thus why would
these not work with the 500 GB disk?

Re: External USB case for 2.5 inch SATA drive

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I'm not sure, but I can tell you that a cheap "Kingwin" adapter (no
case) that I got on sale for about $12 will work for at least a 320GB
drive, although the box does not indicate that there is any size
limitation at all.  (320GB being the largest WD Black laptop drive
that was available when I bought it.)


Re: External USB case for 2.5 inch SATA drive

N8N wrote:
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One of the problems I find with these recent
external drive boxes
is that the cables are very stiff and the
connectors are the same size
as for earlier flexible cables. That puts a lot of
strain on the connectors -
possible trouble ahead.

Re: External USB case for 2.5 inch SATA drive

J G Miller wrote:
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The practice of quoting capacity, is not standardized in any way.
For some companies, the quoted capacity is "what we've tested with".
If the product was designed when a 100GB drive was available,
it'll say "5GB to 100GB capacity".

Your two example products were untraceable. I tried safecom.cn but
even the archives for the site, don't mention SU2-25SJA or SU2B-25SPJA.
It would be fun to research further, if the company in question really
cared about what they've made. I would expect to continue to be
able to download a product manual, even if the stupid thing was
out of production. Many other companies continue to keep
"bread crumbs" on their site, for older products, so we can find
out about them.


Re: External USB case for 2.5 inch SATA drive

On Tuesday, April 27th, 2010 at 23:45:00h -0400, Paul wrote:

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But you do agree that the products are available an
on sale at the vendor's site whose URL I quoted?

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I did check safecom.CN myself before posting, and as you found,
there is no mention in the drop down list of products under support
for these items, or via the search facility.

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Many companies, particularly smaller ones, just drop all mention
of their earlier products from their web site when replacement
new products join their line.  As soon as an item is no longer
in production, as far as the web site is concerned, it is as
if the product never existed.

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I had a feeling that this might be the case but was not 100% certain.

I do not see that there would be anything in the USB / SATA which
would in fact be limiting to the size of the disk within normal
disk size ranges.  Obviously a problem might arise because of
limitations in that interface if it was originally specified for
say a 100 GByte disk and one tried to use a disk 1000 or more times
large in size at some point.

I was hoping somebody with in depth knowledge of USB / SATA
interfaces was going to provide some information on possible
limitations of the size of disk which could be accessed due
to the components themselves used in the interface.

I have now had a response from the vendor whose URL I quoted


   these are limits that we have confirmed with our own and
   independent tests.

   As for the reasons - power consumption may be a factor.
   Some drives function correctly and some do not.

   Also there may be a limit imposed by the chipset itself
   on the device (not 100% sure on this one)


As you can see, they do not really know whether or not
there is a limitation in the chipset.  As for the power
supply, since the box is not powered, it is relying on
the USB cable to provide the power to drive the disk.

Since the capacity of 2.5 inch disks is now 320 - 500 Gbyte
standard (and even Western Digital do their own 500 Gbyte
2.5 inch disk in an external box) I would suspect that
sales of the above boxes would now be minimal and why
SafeCom have discontinued this model.

Suprisingly the vendor has not suggested any alternative
boxes to buy from them.

Having discovered at another site a similar product which also
has an e-SATA interface as well as USB, which is not that much
greated in price, and there is no mention of a limiting disk
size, I am now considering purchasing that instead.

Thank you for your response, which actually addressed the
question which I raised.

Re: External USB case for 2.5 inch SATA drive

J G Miller wrote:
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The only limit I'm aware of, for the disk itself, is the
137GB limit caused by 28 bit versus 48 bit LBA. That was an
IDE issue, which changed sometime around 2003. So any recent
silicon should support 48 bit LBA, and no longer be an issue.
As far as I know, SATA has that by default.

(Article about a chip with that problem, from 2002.)


For the USB controller, I can't think of a reason or
justification for a limit slightly above 137GB. If
a device can do 137GB, it should be able to do 320GB
as well.

There is an example of a USB to IDE chip here, and a
datasheet available on the page as well. I didn't find
a size limit stated in the datasheet. This is the kind
of chip my enclosure uses.


Those chips may have limits, but there might not be
rational reasons for the limits. If a designer chose
to use an 8 bit microprocessor internally, to do
whatever protocol translations are necessary, there
could be any number of firmware bugs. If the function
instead, is implemented in logic gates ("purely mechanical
translation"), then it is less likely for some weird
limit to pop up. It would be more likely to be completely
broken, if there was some tiny error in the design.
Having firmware in a device, leaves more room for

The scheme itself is reasonably complicated. It looks like
SCSI command blocks might be passed in USB packets. The SCSI
command block would need to be converted into values loaded
into command and data registers on the drive. Actual data
transfers could be more mechanical (streamed). I don't really
know how complicated the protocol translation has to be here,
whether you can get by with some very simple sequences, or it is
a complicated flow chart. One benefit of using SCSI at least,
is Microsoft OSes like the SCSI stack for "non-native" storage
devices, so a lot of other storage devices are accessed via
SCSI commands. So for Microsoft to add USB support, at least
some of the work would already have been done. I've never
run into any references of SCSI running into capacity limits
in its commands, yet. So while IDE got stuck at 137GB, SCSI
didn't have the same issue. By the looks of this, it would be
more than a day-long job to trace through the details.




Re: External USB case for 2.5 inch SATA drive

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If your 2.5" drive is only for at home use for backups, etc,
consider something like the Therlmaltake BlacX.  If you're
not familiar with that device, it's an external plug in drive dock.
The unit I have takes 3.5" or 2.5" disks and has USB2, and
eSATA interfaces.  It's great for backups, cloning drives, etc.
Using the eSATA interface, it can also be used for booting OS

I don't know what its max drive capacity is, but it works with
a 1TB drive.  The BlacX has a built in interface for USB2, but
for eSATA, the drive is controlled directly by the motherboard
eSATA controller. It comes with a power brick, and cables
for both interfaces.  This device makes it easy to use multiple
2.5" bare drives as compact backup media. At $100 a drive for
500GB drives, it may seem expensive, but not when you consider
that not much over 10 years ago tape backup cartridges of much
lower capacity, and reliability, could cost that, or more.

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