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I use my old 500gb drive to store all temporary stuff (windows temp folder, adobe scratch disks etc), and anything that needs thousands of small files to avoid unnecessarily fragmenting my C drive. However, it has started slowing down a lot recently (28000 hours of use so maybe it's dying, last year I moved the pagefile back to C as the read/write wait was slowing the entire computer), plus an upgrade would be nice, so I was thinking about getting a 4TB drive for temp files and games.

The only reasonably priced 7200rpm one I found is a Toshiba USB 3.0 external drive, so I'm wondering if USB 3 is sufficient for use such as what I mentioned above? The current 1TB external I have is a bit unreliable and slow, (good for storing media but not much else), so I don't want to risk it without checking first.

Update:
I have the drive, it's read/write speeds are over 50% higher than every other drive I have, and in its current new state, it can write lots of small files faster than my existing drives can. This is also using the PCI to USB 3 extension, not the slots built into the motherboard. I'll update this if anything changes, but the answer to the question is there definitely doesn't appear to be any loss in performance.

Update 2 (1 year later): I'm using it with an SSD for the C drive now, and there have been no problems for at least as long as I've had Windows 10. I'm using it to store around 2.3TB of games, photos, and music, and it's still going fast. Maybe you might not get the same experience, but I'd say it's definitely worth it for saving money.

  • What would be the disk controller used when internal? What is the motherboard that your using? – Psycogeek May 25 '15 at 12:26
  • Not entirely sure about disk controllers in general, but the motherboard is the ASUS P6X58D-E – Peter May 25 '15 at 12:29
  • You might wish to tweak usb turbo mode buffer. Or you could just get eSata+USB3 external disk case (something like this and couple it with Sata-eSata adapter). Slap inside 3.5inch 7200rpm disk and enjoy. You should even save some cash. (All links are randomly googled, no advertising intended) – PTwr May 26 '15 at 6:53
  • In my searches I never came across one in my price range that also had a sata output, but the PCI to USB thing I installed had a turbo mode, so I activated it after seeing your comment, and the drive is running faster than my internal ones. Dunno if it's to do with the turbo mode, but if it does nothing bad, I may as well leave it on :) – Peter May 29 '15 at 1:16
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USB 3.0 has an upper limit around 5.0Gbps. SATA III has an upper limit of 6.0Gbps. Regardless of overhead these rates are far higher than what a mechanical HDD can sustain for large transfers.

Most mechanical HDDs won't be able to sustain more than about 1.5Gbps (HDD Speed results). So I doubt you would notice much difference in performance. Real world performance would be affected more by the HDD, chipset and drivers (be sure to keep your drivers up to date).

Just remember to treat your external HDDS gently. Don't knock them while they're running, this could damage the platters. I still tend to eject my usb disks that I use for backups just to be sure they stay reliable.

  • Thanks, that's good to know, I'll be leaving it next to the PC anyway so it won't be getting knocked :) – Peter May 25 '15 at 12:31
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    Out of curiosity, do you have any references for Instead they run just fast enough to qualify as USB 3.0.? – Ajasja May 25 '15 at 12:44
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    No way usb 3.0 runs as fast as a sata hard drive on the sata bus. If you are lucky you get half of the max design speed on any usb device. – Moab May 25 '15 at 13:39
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    @Moab - not true. It depends what you're comparing to. USB 3 can support up to 5Gbps (inc overhead), that's much quicker than SATA II, but not as fast as SATA III. If you have an SSD drive attached, it'll fly past a drive connected to SATA II. – Matt H May 25 '15 at 20:46
  • @Ajasja I couldn't find any reliable references to back me up my claim that USB 3.0 doesn't run at full speed so I've retracted that statement. – snoopen May 25 '15 at 23:46
9

USB will always be slower than SATA because of protocol overhead, at least. You also must consider that USB is "one transfer at a time", which means any other device connected to USB will degrade performance of the USB-HDD.

While theoretically using 1 USB root for 1 USB hdd might yield good results, in practice every computer has a plethora of other devices connected to USB.

But, even if you buy an external drive (which usually houses the slowest available model), you can always rip open the enclosure and take the hdd out. Unless your computer is a laptop without a 3.5" bay and the external drive is 3.5" (which would explain the price difference). Then an eSATA port would give the best performance.

  • I was looking into taking the drive out the case, but then if it was to die within a month or two I'd have no warranty haha. I've never heard of the 'one transfer at a time' thing with USB though, surely if that was true, the mouse updating like 1000 times per second would stop everything else working, or if you were copying files via USB, it'd stop the mouse working? For the record, I've got a USB 3 card plugged into the PCI slot as well as the slots connected to the motherboard. – Peter May 25 '15 at 13:41
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    @Peter I think the "1 transfer at a time" restriction applies to the protocols used for the transfer of pictures and audio (MTP and PTP), when the host device is "smart" and this allows them to share the use of the disk space with itself as well as with the computer it is connected to - UMS (USB Mass Storage), which is what flash drives and external hard drives use, does support parallel operations. As far as the protocol overhead, USB 3.0 has very little, it's a direct-memory access based protocol, which puts it in the same performance category as SATA/eSATA. – user2813274 May 25 '15 at 15:03
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    This answer brings up some interesting points such as USB root to peripheral limitations. However the "One transfer at a time" comment does not apply as @user2813274 has mentioned. Further as I have mentioned in my answer the maximum speed os USB 3.0 is well above the maximum a mechanical HDD can output. I'd be interested to know how many additional devices on a USB root it takes to degrade the transfer rate. – snoopen May 26 '15 at 4:45
  • I have no idea how widespread this is but I have heard of external USB drives that don't contain a SATA drive in a USB-SATA housing but have the USB interface actually integrated into the drive's electronics - so you would not be able to remove this kind of drive and use it on an eSATA port. – nekomatic May 26 '15 at 7:25
  • @nekomatic I think it's pretty rare. Most drives I know are indeed regular hdd with usb-sata circuit snapped on. It's usually uneconomical to produce dedicated usb hdd. You can always search for videos of "name-of-your-drive disassembly" and see for yourself, eg: google.com/… or google.com/search?q=Toshiba+USB+3.0+external+drive+disassembly – Agent_L May 26 '15 at 9:22
3

This answer is getting criticized...
The main support to my answer is my personal experience: in the last 12 years I've used many usb 2.0 / 3.0 external HDD for backup purpose. In my direct experience external usb drive have always been waaaay slower that internal drive. I know that when I need to backup 1 o 2 Tb worth of data to an external usb drive (doesn't matter if it's a 3.0 usb) the only way to do it fast, is dismantle the usb drive, and attach the HDD directly to the PC via ata/sata.

This is just my experience, but maybe I'm overlooked something...
this night I'll try to get some numbers to support my claims.

Update: At the moment I don't have external USB 3.0 drive, just old usb 2.0 HDD case, and new eSata HDD case, so I'm unable to produce any useful data to support my claim.
(clearly I'll try to produce some data whenever I find a spare usb 3.0 case)


Original answer:

Sorry but NO, an external USB 3.0 drive can be waaaay slower that an internal drive.
This is especially true if you have many small files.

I know this from my experience, because I use external drive as a backup, and any external USB drive is waaaaaay slower that an internal drive, or an external eSata drive.

To support my claim I've just made a simple test: try copy 10'000 small files to both external and internal storage. (each file is 400 bytes)

For external storage I've used a Sandisk Extreme Plus 128Gb flash card (it write data at 80Mb/sec, faster than many mechanical HDD, and no moving parts...)

For internal storage I've used a 1Tb sata HDD (Samsung HD103UJ).

Copy 10000 files the external SD via USB 3.0 took 150 seconds (66 files/sec - 0.03 Mb/sec).
Copy 10000 files the internal HDD via sata took 3 seconds (3333 files/Sec - 1.30 Mb/sec).

So, using an external HDD connected with Usb 3.0 is ok if you have few big files.
But if you have many small files, of if you plan to use the external drive as a backup, be prepared to wait long time.
(on my boot HDD I have about 484'000 files... copying these on an USB drive at 66 files/Sec would take more than 2 hours if all these file where just 0.5kb each)

  • So, which filesystem are we talking about? Probably exFAT. exFAT is painfully slow for small files, and so are SD cards, because they usually have an erase block size of at least 128 Kilobyte. Additionally, SD cards are optimized for linear access, because that’s what happens when storing videos or photos. I actually tried it and it was fast enough: 20 seconds. Your over-dramatizing things. – Daniel B May 28 '15 at 21:21
  • Oh yeah, almost forgot: Local disks also use write caching by default, which further distorts your test results. – Daniel B May 28 '15 at 21:30
  • Well, I would have guessed an SD card would be slower haha, but I was getting a external physical drive, not SD. I got the drive now anyway, it's main read/write speeds are faster than all my internal ones (internal ones are 80mb/s, ext is 140mb/s). I did a test with copying 8k 400 byte files off C, both the internal and external drives copied them in 8 seconds. When copying 35k image tiles off the other internal drive, my C drive was taking 11 minutes to copy it while the external was taking 4. – Peter May 29 '15 at 0:51
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Computers are only as fast as their slowest component, and in the case of external HDD vs. internal HDD the slowest component is the hard drive itself, not the transfer bridge (i.e. USB 3 or SATA 3).

The specs of the drive inside the external is what you need to focus on, and same goes with the internal. Be sure it has a low seek time (the lower the better) and that it has a nice size buffer (the larger the better) and the higher the spin rate (more rpm is better) the better.

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