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I plan to replace my laptop's 5400rpm HDD with an SSD in the near future. I then want to make the old HDD an external HDD. I want to get it to work with USB 3.0.

  1. Will I get better speeds from my 5400rpm hard drive when it is inside an enclosure providing USB 3.0 connectivity?
  2. what will the possible speeds be?
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4  
Just a tip in case you've not thought about it. You can also replace DVD drive with Hard Disk in some laptop (Google Hard Drive Caddy) – VarunAgw Mar 15 at 21:57
    
@VarunAgw That is so awesome! Never heard about that before! But unfortunately my laptop doesn't have an optical drive. I'm already using an external one. But thanks! That's really cool! – Mentos93 Mar 15 at 22:11
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Please not that at least some USB enclosures mess with sector numbering, which means you can't use the HD in the enclosure without reformatting. This has happened more than once to me; be sure you have a backup of your original HD. – Guntram Blohm Mar 15 at 22:28
    
Actually tried this while going from a 5400RPM 1TB HDD to a 120GB SSD... HDD runs as fast as it used to on SATA with USB3. SSD is damn fast though. – ardaozkal Mar 16 at 15:15
    
@VarunAgw that is the best choice if your PC supports it, and is easy. My laptop requires ten minutes of taking it apart to reach the Optical Drive, but about 2 minutes to reach HDD/SSD. – ardaozkal Mar 16 at 15:17
up vote 32 down vote accepted

Will I get better speeds from my 5400rpm hard drive when it is inside an enclosure providing USB 3.0 connectivity?

That depends what you are comparing it with. Speeds over USB (1 or 2 or 3) will be slower than directly in the laptop since you are adding protocol overhead.

Or what will the possible speeds be?

Assuming that the drive is fast enough (and most 5400 RPM laptop drives seem to yield read speeds of about 90Mb/sec and slightly lower write speeds) then you will get:

  • Internal: 90MB/sec
  • External eSATA: 90MB/sec
  • External USB2: about 30-35MB/sec (limited by USB 2 speed)
  • External USB3.0 / USB3.1 gen 1 (5.0Gbit/sec): About 10x the speed from USB2. Which probably comes close to the speed of the disk when used internally with a direct SATA connection minus overhead.
  • External USB3.1 gen 2 (10.0Gbit/sec): Doubles the bandwidth of USB3.0 / USB3.1 gen 1. Since your disk is probably the slowest part this does not increase performance
  • External USB3 with UASP support: Significantly less overhead, but probably still limited to the same speed due as the previous one because the disk cannot saturate the channel.


That was a lot of text, now to a practical answer :)

A laptop drive is usually significantly slower than USB3's transfer speed. So you get almost the same speed when you use a slow laptop disk in an USB case as when you use it internally.

If you still need to buy an external case: Look for one which supports UAS[P].

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Thank you very much for your clear answer. I've up voted and accept the answer. Up vote will display as soon as I've reached 15 reputation. But thanks, will look for the UAS[P]. – Mentos93 Mar 15 at 13:12
    
Upvote from me as well, for both the answer and question. Lets get @Mentos93 his 15 rep points. :) – LPChip Mar 15 at 13:25
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A bit of trivia: I myself am using a USB 3 enclosure (ICY BOX IB-112StU3-B to be exact) for my 5400 RPM hard drives. I usually get around 50 MB/s from few WD6400BPVT hard drives I have and around 85 MB/s from an ancient SSD I have. – AndrejaKo Mar 15 at 14:26
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Shouldn't it be "SCSI over USB"? Sounds better that way ;p – PTwr Mar 15 at 14:32
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My experience with USB2 enclosures is that a very common implementation seems to have a hard limit of 20MB/s. They often quote the usb2 maximum transport speed on the box, which is irrelevant. – JDługosz Mar 16 at 2:38

When I was using USB 2.0 docking station with the server grade hard drive, the speeds were never above 40 Mb/s, while the same drive on the same machine was capable of 100 - 120 Mb/s when connected through SATA II.

I am not sure why this protocol overhead (USB 2.0 has the advertised speed of 60 Mb/s), but may fully be that USB 3.0 has less of it, and the drive will show better performance.

Accessing the drives internal RAM cache may be much faster through USB 3.0. This may have significant impact if you read lots of the same small files repeatedly, but also may not have as another RAM cache is provided by the operating system itself.

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The 480Mbit is the wire speed, without protocol overhead and without encoding. This is why actual data transfer will never reach the advertised speed). – Hennes Mar 16 at 8:36
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Also Mb/s != MB/s; 480Mb/s = 60MB/s (where b = bits and B = Bytes) – Tom Yan Mar 16 at 8:38
    
Corrected to 60 – h22 Mar 16 at 8:40
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Btw the one of the major factors that constitutes the overhead is the 8b/10b encoding, so 480Mb/s * 8 / 10 = 384 Mb/s = 48MB/s. Therefore if you can get 3x ~ 4x MB/s out of USB 2.0 it is actually already a pretty ideal case (considering this bandwidth is often shared by all the ports, and other factors): en.wikipedia.org/wiki/8b/10b_encoding. This has not been changed until USB 3.1. which adopted the 128b/132b encoding scheme: en.wikipedia.org/wiki/USB#USB_3.1 – Tom Yan Mar 16 at 8:48

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