bitequator

Pocket storage recommendations?

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The max capacities of the different HDD formfactors that I've been able to find are listed below (thanks to this forum). Corrections/additions much appreciated.

1" 3600rpm formfactor: 5-8GB max?

- pocket USB drives (like this) or MicroDrive/CF cards (like this)

1.8" 4200rpm formfactor: 60GB max (Hitachi), soon 80GB (Hitachi)

- smallest USB enclosure: 3.2" x 2.8" x 0.4" @ 1.9oz (like this)

2.5" 4200rpm formfactor: 120GB max (Hitachi)

2.5" 5400rpm formfactor: 120GB max (Seagate), soon 160GB (Seagate)

2.5" 7200rpm formfactor: 100GB max (Hitachi, Seagate)

- smallest USB enclosure: 4.5" x 2.6" x 0.4" @ 2.2oz (like this -- 9.5mm height only)

3.5" 7200rpm formfactor: 400GB max, soon 500GB (Hitachi, Maxtor, Seagate)

- smallest USB enclosure: ?

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I'm already using the 1.8" 60GB Hitachi Travelstar C4K60 drive (with IDE connector) in a USB enclosure. I wish the 1.8" 80GB slim Travelstar is already out (and that my 1.8" USB enclosure supports ZIF connector in addition to IDE).

I'm now thinking I should wait for the 2.5" 160GB (5400rpm) Seagate Momentus 5400.3 to come out and stick that in a slightly bigger 2.5" USB enclosure. But when will it be out? Heck, most places don't even have the 120GB Momentus 5400.2 yet, though I imagine I will be able to get this much sooner than the 5400.3.

Or, should I go for the 100GB 7200rpm 2.5" drives (Seagate Momentus 7200.1 or Hitachi Travelstar 7K100)? Besides having smaller capacity, my biggest concern is that these 7200rpm 2.5" drives require so much power that some computers may not be able to supply enough USB bus power??

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Hmm, I took a closer look at some of the power specs and the peak startup requirements have me worried now :huh:

AFAIK max USB bus power is 5V at 500mA (= 2.5VA, or simplistically 2.5W).

My Travelstar C4K60 1.8" drive is fine because its peak startup power draw is listed at 2.1W.

But while the 2.5" drives I mentioned have seek/read/write/idle/standby power draw within the USB limit for the most part, the peak startup requirements range from 4.5W to 5.5W (ie. 0.9A to 1.1A current)!

I do remember from experience with previous 2.5" USB drives that it's the initial spin-up peak power draw that's the killer. How could such USB drives be advertised to run off USB bus power, when they require twice as much as the maximum USB power limit to start up in the first place??

I assume for these drives that you would always need the dual-head USB power cable (to draw 2.5W from each USB port)? But once the drive is running, could you then pull out one of the USB cable leads? :)

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If someone were to be a bit creative with the power suppy of the external USB chassis there is no reason that a 2.5" drive would be any problem. The excessive current only lasts for 2 seconds. Mind you I have not seen any external chassis that has this kind of power supply but it would be an interesting little design project to do.

^ BTW the 2.5" HDD power draw I mentioned above refer to all the models that I've found (from 4200rpm to 7200rpm).  Maybe I should just stick to 1.8" USB drives?

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I also posted on the ThinkPads forum:

http://forum.thinkpads.com/viewtopic.php?t=13348#86416

Discussing size/weight/capacity trade-offs:

Hehe yeah, I'd seen that round Seagate 5GB USB pocket HDD at CompUSA and other places.  Just to make it clear for others, that's a prepackaged product (I don't think you can just open the enclosure and take out the drive modularly).

Unfortunately, even if it uses a small 0.85" 5GB HDD, that thing is already 3" (diameter) x 0.7" @ 2.2oz.

Whereas my 1.8" 60GB HDD in a modular USB enclosure is 3.2" x 2.8" x 0.4" @ 4oz and provides 12 times the capacity!

Granted the Seagate 1" (0.85") 5GB USB pocket HDD does have some advantages:

- lighter weight

- built-in retractable USB cable (I'm using a separate retractable ZipLinq/Boxwave USB cable)

- probably more cushioning for better protection

There ARE prepackaged 1.8" USB HDDs like the:

- Targus 40GB (3.4" x 3" x 0.6" @ 3.2oz)

- Apricorn 60GB (3.9" x 2.8" x 0.6" @ 5oz)

which also come with a short built-in USB cable, but they're usually bigger, heavier and much more expensive than the modular enclosure solution I'm using.

Besides, with the modular solution I thought I could always take out the HDD in the future and stick it in my X-series ThinkPad notebooks (that is, until you mentioned that the X-series uses custom 1.8" drives with proprietary connector?).

As far as CF Microdrive HDDs, I've been able to stay away from them and just get by with my three 2GB 60x SD cards (along with my three 1GB and a few smaller capacity SD cards) :)

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If someone were to be a bit creative with the power suppy of the external USB chassis there is no reason that a 2.5" drive would be any problem. The excessive current only lasts for 2 seconds. Mind you I have not seen any external chassis that has this kind of power supply but it would be an interesting little design project to do.

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Wow sounds awesome, do you mean we just need the USB drive enclosure to have something that can accumulate power for a short time and discharge it in a short burst to provide for the drive's spin-up peak power draw??

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Wow sounds awesome, do you mean we just need the USB drive enclosure to have something that can accumulate power for a short time and discharge it in a short burst to provide for the drive's spin-up peak power draw??

211828[/snapback]

That is the basic concept. The components for this kind of design have become common the last couple of years. I had looked at this kind of problem / solution in a different context but never did anything with the idea.

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Wow sounds awesome, do you mean we just need the USB drive enclosure to have something that can accumulate power for a short time and discharge it in a short burst to provide for the drive's spin-up peak power draw??

211828[/snapback]

That is the basic concept. The components for this kind of design have become common the last couple of years. I had looked at this kind of problem / solution in a different context but never did anything with the idea.

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Sounds like a great idea. I wonder if a set of AAA or coin-cell batteries can be used instead... If it is possible, the batteries should last for awhile since they would only be used during the 2-second peak spin-up power draw as you said (or even just to add to the USB 2.5W bus power during that peak power draw)...

Anyways, I wish one of the following has come to pass:

- the original USB specs had specified higher current output (ex. 1A) rather than 500mA

- the USB PlusPower (or "Powered USB") extended specs has become ubiquitous, providing for up to 6A at 5V/12V/24V.

(As it stands, this extended USB port is present in all of our IBM ThinkPad notebooks!)

- powered 1394/FireWire has become as ubiquitous as USB ;)

Barring that, why can't 2.5" HDD manufacturers find a way to reduce the spin-up peak power draw to below 2.5W?

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To summarize my preferences for pocket USB HDDs at this point (cut-n-pasted from the other forum):

Anyways, I like my current Hitachi 60GB/4200rpm 1.8" HDD in a modular USB enclosure (3.2" x 2.8" x 0.4"), which can always run off USB bus power from just 1 port since startup peak power draw is just 2.1W.  It's just that I want more capacity (FYI Hitachi will have 80GB 1.8" model soon).

I can get more capacity with 2.5" HDDs, but their startup peak power draw seem to necessitate always using 2 USB ports :(  If I can live with that, I was going to use one of the following 2.5" drives in a modular USB enclosure (4.5" x 2.6" x 0.4"):

- Hitachi's 120GB/4200rpm model (slower; startup power draw is only 4.5W)

- Seagate's 120GB/5400rpm model or wait for their upcoming 160GB/5400rpm model (faster; startup power draw is 5W or exactly the bus power of 2 USB ports)

Hitachi's 5400rpm models max out at only 100GB.  As for Hitachi's and Seagate's 7200rpm 2.5" drives, their startup power draw is 5.5W which I'm worried is more than many computers can supply even from 2 USB ports.

P.S.  What's ironic is that other than startup, the actual running operations of the 2.5" HDDs (seek/read/write/idle/standby) don't generally exceed the bus power of just 1 USB port!

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Well I found out from this thread that the Seagate Momentus 5400.3 (160GB 5400rpm 2.5" HDD) won't be out until winter! So the only large-capacity Seagate choice for now is the Momentus 5400.2 (120GB 5400rpm).

And the Hitachi Travelstar 4K120 (120GB 4200rpm 2.5" HDD) was just announced earlier this month, with expected channel availability next month.

Which of these two (5400.2 vs. 4K120) is more recommended as a pocket USB drive??

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Curse you!

Now you having me thinking about what it would take to design a pocket storage device with an advanced power supply.

I have done several USB designs so I even have the tools and background for it.

:P

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Hmm, I took a closer look at some of the power specs and the peak startup requirements have me worried now :huh:

AFAIK max USB bus power is 5V at 500mA (= 2.5VA, or simplistically 2.5W).

My Travelstar C4K60 1.8" drive is fine because its peak startup power draw is listed at 2.1W.

But while the 2.5" drives I mentioned have seek/read/write/idle/standby power draw within the USB limit for the most part, the peak startup requirements range from 4.5W to 5.5W (ie. 0.9A to 1.1A current)!

I do remember from experience with previous 2.5" USB drives that it's the initial spin-up peak power draw that's the killer.  How could such USB drives be advertised to run off USB bus power, when they require twice as much as the maximum USB power limit to start up in the first place??

I assume for these drives that you would always need the dual-head USB power cable (to draw 2.5W from each USB port)?  But once the drive is running, could you then pull out one of the USB cable leads? :)

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The fun part is that it's 2.5W per bus (and on most computers, each port is a separate bus.) I have a USB enclosure that has a 'Y' near the end and has a second USB plus on it. (With a female plug as well, so it acts as a pass-through.) This second plug only provides power to the enclosure, but it means that with both the main data USB plug, and this extra power plug, you can draw up to 5W. (In fact, the enclosure mentioned in the first post seems to be the same enclosure I'm talking about.) That, combined with the 'USB Power Plus' mentioned earlier solves it. (In fact, on my enclosure, I don't need the extra USB when connecting to most USB 2.0 ports, as most USB 2.0 are 'Power Plus', but I do need it on my PowerBook, which only has lower-power USB 1.1.)

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Are there any references to "Power Plus" other than http://www.usbpluspower.org ? This modification of the USB standard does not seem to be all that common. It requires a special connector containing a second set of wires for high power.

I cant find any reference to higher power operation in the USB standard documents.

The Y cables may work but they really don't meet USB spec.

The fun part is that it's 2.5W per bus (and on most computers, each port is a separate bus.)  I have a USB enclosure that has a 'Y' near the end and has a second USB plus on it.  (With a female plug as well, so it acts as a pass-through.)  This second plug only provides power to the enclosure, but it means that with both the main data USB plug, and this extra power plug, you can draw up to 5W.  (In fact, the enclosure mentioned in the first post seems to be the same enclosure I'm talking about.)  That, combined with the 'USB Power Plus' mentioned earlier solves it.  (In fact, on my enclosure, I don't need the extra USB when connecting to most USB 2.0 ports, as most USB 2.0 are 'Power Plus', but I do need it on my PowerBook, which only has lower-power USB 1.1.)

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Yeah, I think the USB PlusPower port on our IBM ThinkPad notebooks does feature a "second" special connector stacked on top of the normal USB connector on the bottom, so that USB PlusPower cables would attach to both connectors, but normal USB cables can still attach to just the bottom one. But you're right, I haven't seen this PlusPower combo connector anywhere else.

What's interesting though, my ThinkPad X40 notebook has that USB PlusPower combo connector on the left side, a standard USB connector on the right side, and three standard USB connectors on the docking station base. And the thing is, I can run my various 2.5" USB hard drives from just a single USB port using any of these USB connectors (whereas these hard drives often fail to spin up using a single USB 2.0 port on the majority of desktop PCs that I'd tried)!

Which means IBM must design all the USB ports on their ThinkPads to supply at least 5W of power each, with the USB PlusPower port supplying even more (because IBM does offer various optical burner drives that require the PlusPower port to run). I find that interesting and wish more hardware manufacturers design their USB ports to exceed the 2.5W standard specs. I had thought doing so might damage some other USB peripherals, but I don't think IBM would have done it if they knew it would be damaging (and I certainly haven't come across any situation where any USB peripheral was damaged as a result of attaching to my ThinkPad).

Edited by bitequator

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Anyways, I'm still trying to decide which 2.5" HDD (for a USB enclosure) I should get. I want the biggest capacity I can afford in the smallest possible size, with the most chance of being able to run from (dual-port) USB bus power.

The 120GB Seagate Momentus 5400.2 2.5" drive (5400rpm, 8MB cache) is now in stock for $260, whereas most of the 100GB 5400rpm notebook drives from that same vendor sell for about $170. That's $90 difference just to get an extra 20GB (the largest available capacity in 2.5" formfactor)!

So the first question is: is it worth it to splurge on the 120GB capacity?

Alternatively, I can wait for the 120GB Hitachi Travelstar 4K120 2.5" drive (4200rpm, 8MB cache) which is supposed to be available in the channel this month. The reason I ask is that the Hitachi 4K120 only requires 4.5W startup peak power whereas the Seagate 5400.2 requires 5W power. I'm afraid that combined with the IDE-to-USB adapter, the power draw for the Seagate in a USB enclosure might be on the borderline of being just a bit too much than can be supplied by 2 USB ports on some computers?

So the second question is: should I get the Seagate or Hitachi?

Edited by bitequator

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BTW, I'd wanted to ask why there are different part numbers for the various Seagate Momentus 5400.2 hard drives.

For example, for the 100GB capacity, PriceGrabber lists 2 different part numbers:

ST9100823A

ST9100824A

With the second one usually a bit more expensive...

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Seagate's article on "Finding the Ideal Disk Drive for 2.5-Inch External USB Applications":

http://www.seagate.com/docs/pdf/whitepaper/TP-535.pdf

It might include some marketing speech but it has some facts about Y-cables, USB-ports, etc. It also has some graphs depicting power draw of several drives of different manufacturer's and rpm.

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Seagate's article on "Finding the Ideal Disk Drive for 2.5-Inch External USB Applications":

http://www.seagate.com/docs/pdf/whitepaper/TP-535.pdf

It might include some marketing speech but it has some facts about Y-cables, USB-ports, etc. It also has some graphs depicting power draw of several drives of different manufacturer's and rpm.

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If this information is representative of what USB drive chassis' expect to see out of a

USB port it is surprising that the devices work as well as they do. When I was designing

USB bus powered devices I spent a lot of time making sure that my designs would fit

into the 500ma current budget. I guess the only thing to say is praise be to the over

engineering of the host ports.

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USB ports are protected with a fuse (poly switch) that limits current.

They are 0.6A per port, or 1.1A per two ports. The latter can spin up one 2.5" drive.

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Wow thanks a lot for all the info guys! I really like that Seagate whitepaper for discussing the things I'd wondered about (as a layperson). I didn't know about many of the listed facts about USB port power specs in the real world.

I've ordered that Seagate 120GB 2.5" drive for my USB enclosure (to complement my Hitachi 60GB 1.8" USB drive). Perhaps in the future I'll be able to afford to upgrade to the 80GB 1.8" and 160GB 2.5" drives...

Next I will try to find the smallest USB enclosure for a 3.5" drive (with the smallest power brick/cable), and try to find a good 500GB drive for it. Anyone got any recommendations?

P.S. Up to now I've been using mostly Addonics drive trays/enclosures for 3.5" and 2.5" drives. These enclosures can use USB2, 1394, PCMCIA/CardBus, SATA interface cables when used externally, and additionally can be used as IDE drive trays when you install the dock/frame in the computer bay. In fact all my home desktop PCs use such removable trays for all the hard drives (I'd been obsessed about that, especially for the RAID setups). But for portable use these enclosures are not the smallest, nor the most convenient (since you have to bring one of their proprietary interface cables).

Edited by bitequator

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Next I will try to find the smallest USB enclosure for a 3.5" drive (with the smallest power brick/cable)

212415[/snapback]

I forgot to say, I guess the smallest 3.5" USB enclosure... is no enclosure (ie. using the naked hard drive with a USB-IDE adapter cable) :)

I've been using this and quite like it as an alternative to an enclosure (assuming the naked drive can withstand the rigors of external use)...

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Well for a 3.5" drive I ordered the 500GB Hitachi 7K500 (though the 500GB Seagate 7200.9 is supposed to come out soon).

Interestingly with regards to 2.5" drives, NewEgg has also started stocking a 120GB Toshiba MK1233GAS (4200rpm, 8MB cache) for about the same price as the 120GB Seagate Momentus 5400.2 (5400rpm, 8MB cache). I couldn't find this new Toshiba model listed on their corporate website, but based on data sheet for previous model I'd guess it draws 4.5W at peak spin-up. I wonder how this new 2.5" Toshiba drive compares to the upcoming 120GB Hitachi 4K120 (4200rpm, 8MB cache), and whether I should cancel my Seagate 5400.2 order and go for the Toshiba instead...

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Anyways, to quote some interesting statements from the abovementioned Seagate whitepaper on USB hard drives:

A common problem with 2.5-inch drives in an external USB application is the drive’s ability to spin up from the current coming off of a single USB cable. Some drives require the use of a second USB cable or even a separate power supply, while others are more power efficient and able to operate from a single USB cable. However, the USB port can also play a role in the drive’s ability to spin up off a single cable.

The USB 1.1 and 2.0 specification requires that each USB port delivers at least 500 mA of steady-state current; however the majority of systems provide 700 mA of steady-state current. Most 2.5-inch disc drives meet this requirement only after they are already spinning and usually require a higher current during the initial spin-up profile. The majority of USB ports also allows for a higher current draw of 1000 to 1100 mA for a limited duration (instantaneous current) that allows the disc drive to spin up adequately. This capability varies from PC to PC and depends on a variety of factors such as the type of USB port, the USB controller used, the type of regulator and the type of capacitors at the host.

On most disc drives, the maximum power draw is during the initial few seconds, during which the internal disc pack within the drive is being spun up to the full operational speed. In the design of disc drives, there is a temptation to minimize spin-up time at the expense of the maximum current draw during this time period. For external USB drives, however, maximum current consumed is a much more important parameter than spin-up time.

To ensure that external devices can be powered by USB, many external-case manufacturers include a "Y" cable so a minimum supply of 1000 mA is available to the disc drive; however, this is not always required.

Since it is not possible to validate that any particular disc drive works in all USB boxes, it is important to know which disc drive is best optimized for startup current.

The chart in Figure 2 shows the peak 5V current draw by several drives during the spin-up process. Among the drives tested, the maximum current draw ranges from 818 mA to 1147 mA instantaneous current. Drives with peak current below 1000 mA is most ideal for external USB applications.

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