Hard drive enclosures

Hard drive enclosures - 20/03/2006 18:58

You know those USB/Firewire laptop hard drive enclosures that claim you can use the usb as its power source...

is that always the case? Should I stick to a certain capacity and rpm to ensure no issues?

Also does anyone recommend a nice enclosure? Preferably small as possible, aluminium.

Posted by: robricc

Re: Hard drive enclosures - 20/03/2006 19:22

I have a few of these and they work great. The supplied USB cable has two plugs on one end so you don't have to power the drive from a single port.

Posted by: matthew_k

Re: Hard drive enclosures - 20/03/2006 19:26

It's always been the case for me, with the exception of one really old laptop drive that wouldn't have fit in the enclosure in the first place. You do have to use the double ended USB cable, as usb ports are speced at .5watts, and the drives pull 1 watt. Many computers will regulate these to prevent you from killing the motherboard, which is what leads to the working on some computers and not on others. Firewire ports provide the full watt the drive needs, AFAIK.

Matthew

Posted by: wfaulk

Re: Hard drive enclosures - 20/03/2006 20:37

Not all Firewire ports are powered, however. The tiny 4-pin ones don't carry power, while the regular pentagonal 6-pin connectors do.

Posted by: CrackersMcCheese

Re: Hard drive enclosures - 20/03/2006 20:40

Ok, so Rob do you need to use the 2 ports for all your drives?

Posted by: robricc

Re: Hard drive enclosures - 20/03/2006 21:50

The drives I use (displaced Travelstars from upgraded empegs) don't appear to requite both plugs. But, this may just be my laptop and desktop machines allowing more power being drawn though a single port. If I can, I plug in both to be safe.

Posted by: peter

Re: Hard drive enclosures - 21/03/2006 14:55

Quote:
I plug in both to be safe.

Of course, unless the device enumerates separately on both ports and is awarded 500mW by the PC on each, you aren't technically any safer. A pint says no enclosure in the world bothers doing this (do you see two USB devices in Windows?).

Peter

Posted by: robricc

Re: Hard drive enclosures - 21/03/2006 15:14

No, You don't see two devices. What do you want for $10?

Posted by: mlord

Re: Hard drive enclosures - 21/03/2006 20:05

Quote:
Quote:
I plug in both to be safe.

Of course, unless the device enumerates separately on both ports and is awarded 500mW by the PC on each, you aren't technically any safer. A pint says no enclosure in the world bothers doing this (do you see two USB devices in Windows?).

I use these double-plug devices, and can confirm that they do indeed get full power from both plugs. So they work.

I have a ThinkPad A21p notebook that will NOT work with external USB drives unless they're self-powered -- the machine has only one USB port (1.1), so there's nowhere for the second plug to go to help matters.

But all of our other multi-port USB machines work fine with the double plug cables. One of the two plugs is for power-only, and has no signal wires; the other has both power+signal. Plugging *either* one into any machine here causes the attached drive to spin up.

So I usually remember to plug both into the PC first, and then plug the "B" end (actually an A plug) into the USB enclosure. Wouldn't want to fry something inside my notebook! Some Apple notebooks had that problem once (burned out USB traces on mainboard due to drive startup current). I think Drakino suffered from that once.

Cheers

Posted by: wfaulk

Re: Hard drive enclosures - 21/03/2006 20:19

I think the point is that in the USB handshake, it actually tells the computer how much power it's taking so that the computer can allocate power properly. If it just sucks power without telling the computer, it might oversubscribe the power.

Or I could just be making shit up.

Posted by: n2toh

Re: Hard drive enclosures - 21/03/2006 20:19

Quote:
Quote:
I plug in both to be safe.

Of course, unless the device enumerates separately on both ports and is awarded 500mW by the PC on each, you aren't technically any safer. A pint says no enclosure in the world bothers doing this (do you see two USB devices in Windows?).

Peter

It's 500mA per port not 500mW. as can se seen here as for what the voltage is I've seen both 5 volts and 2.7 to 3.3 volts speced on different whitepapers. So the worst case power available for devices is 1.35W or 2.5W with a 5 volt supply.

Posted by: tman

Re: Hard drive enclosures - 21/03/2006 20:58

USB supply voltage is always 5V +/- 0.25V. If it said anything else on a whitepaper then it is seriously wrong.

The voltages used for signalling are odd however.

Posted by: Attack

Re: Hard drive enclosures - 21/03/2006 21:06

I have this one from Compusa and it only has one USB cable and not external power cable. I've got a 60GB Travelstar in it and it works on every PC / laptop I've tried to use it with.

Posted by: mlord

Re: Hard drive enclosures - 21/03/2006 21:16

Quote:
I think the point is that in the USB handshake, it actually tells the computer how much power it's taking so that the computer can allocate power properly. If it just sucks power without telling the computer, it might oversubscribe the power.

Each port must supply 500mA at +5VDC, so there's no oversubscription.

And they have to supply that power before anything is plugged in, since the device needs to power up to talk to the host to tell how much power it really needs.

So one port will be reporting a full draw of 500mA presumably, and the other port will just behave as if nothing is connected to it.. drawing up to 500mA regardless.

This is mostly just for spin-up current. Once spinning, 500mA is about what most notebook drives need to keep spinning (2.5W or so).

Cheers

Posted by: wfaulk

Re: Hard drive enclosures - 21/03/2006 21:32

Right, but what if that other port gets something else connected to it? I'm not an expert on the subject by any means, but isn't it possible that since the USB controller doesn't know about the unsubscribed power consumption it might end up with too much current? I'm thinking specifically of unpowered hubs here.

Posted by: mlord

Re: Hard drive enclosures - 21/03/2006 21:36

Quote:
Right, but what if that other port gets something else connected to it?

It can't. There's a connector already plugged in. No room for another.

But yes, it can blow the budget for other ports on an unpowered hub.

Cheers

Posted by: n2toh

Re: Hard drive enclosures - 21/03/2006 21:43

so if most laptop drives only need about 2.5 watts to run and a slug of power for spinup why not add some sort of energy storage device to supply that slug of power, and onlyu use one USB connector.

Posted by: tman

Re: Hard drive enclosures - 21/03/2006 21:49

Quote:
And they have to supply that power before anything is plugged in, since the device needs to power up to talk to the host to tell how much power it really needs.

When you initially plug something in, a USB device can only draw a maximum of 100mA without telling the host that it wants more. Unless the USB enclosure only needs 100mA on the second plug, it will violate the USB specification.

Posted by: matthew_k

Re: Hard drive enclosures - 21/03/2006 22:00

Gosh, I sure hope my USB lava lamp isn't in violation of the specs. I'd hate to not be able to use it.

Matthew

Posted by: tman

Re: Hard drive enclosures - 21/03/2006 22:28

Nah. Thats in the specs. You have to read it with a blacklight tho

Posted by: mlord

Re: Hard drive enclosures - 21/03/2006 23:01

Quote:
Quote:
And they have to supply that power before anything is plugged in, since the device needs to power up to talk to the host to tell how much power it really needs.

When you initially plug something in, a USB device can only draw a maximum of 100mA without telling the host that it wants more. Unless the USB enclosure only needs 100mA on the second plug, it will violate the USB specification.

Ack. A clear violation, then. Good thing the laptop makers know about it and provide for it these days!

Cheers