Is USB 3 equal to SATA-II or eSATA?

If you look at my other post here, I'm limited to SATA-II on my laptop.
However, I also have an USB3 port.
If I buy a high-performance SATA-III SSD (like the Samsung 240), I know I'll never be able to fully use its speed, but looking only at performance, what is the best (or are they equal):
- SATA-III SSD (240Gb) internal using SATA-II interface
- SATA-III SSD (120Gb) external using eSATA interface
- SATA-III SSD (120Gb) external using USB3 interface

All used as system drives (either as windows 8 normal installation or windows 8 on-the-go installation).

P.S.: I know it doesn't make much sense the external hard drives being smaller than the internal, but if it's external I really don't need that much capacity.
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  1. Best answer
    Performance wise SATA-II has a maximum transfer speed of 3Gbit/s and the eSATA on your computer will likely be the same speed. USB3.0 will actually be faster as it can reach up to 5Gbit/s speeds. (All theoretical maximums, actual speeds are lower)

    So USB3.0 would be the fastest interface of the three in terms of transfer speeds.

    However that's only transfer speeds, latency times are lower for SATA and eSATA.

    So even though the SATA II interfaces would bottleneck a fast SSD more in terms of moving large files, i would still recommend putting the drive in your internal SATA interface, as low latency is quite important for a boot drive. External drives are best used as storage drives

    Long story short, get the internal drive. It will also save you of the mess with external drives every time you want to boot your computer.
  2. You best bet is the internal SSD. In the real world you notice very little difference running SATA3 on SATA2, as most of the real improvement is access time, features, and transfers not improved by the II/III interface. Second, 240Gb SSD's are typically faster than 120. Third, no on your list, but it's internal, easy. Fourth, at best eSATA would be as fast, but no faster than the SATA of the same system (all else being equal) and usually needs additional power. Last, while USB3.0 has the advantage of not needing addition power vs. eSATA, it has yet to reach anything near it's theoretical speeds, and in the end is still a SATAII/III drive, but with additional USB3.0 limitations.
  3. Thanks for your answers, but actually in my system, USB 3 would be much easier (there are a lot of other variables I didn't mention), as well as cheaper (since I only need 120Gb).
    So my real question is performance, for everything else I know usb3 is the correct choice.
    About performance, let me rephrase a little.
    Since I will be limited to sata-II or usb3 speeds and this SSD is (according to most benchmarks I see) capable of surpassing sata-II and usb3, I assume I'll always use whatever interface at its fullest.
    latency is what worries me, is there really a noticeable difference between usb3 and sata in a system drive?
  4. Don't use USB 3.0 as system boot drive. The USB 3.0 controller is not as stable as SATA controller. Time out and dropping a drive will make your OS unstable to use.
  5. USB3.0 is definatly easy to use, and I can't wait for the day when real world speeds catch up to the theoritical. You are correct that the SATA interface with limit your SSD speed, but USB3 is often limited by the various controller and chips in each stage of the interface connection, often giving you much lower speeds in real life than the theoretical speed of USB3.0. As far as latency, it's still and SSD connected to SATAII, adding a USB3 interface on top of that can only increase it, unless its an old SSD (or mislabeled flash drive) with a native USB3 interface (need exact model) which is rare these days.
  6. My 3 TB Seagate Expansion USB 3 (7200 RPM/64 MB cache; NB no "backup" in name) to/from Sandisk Extreme 240 GB throughtputs > 130 Mb/sec. Slow drive transfer rates are unacceptable for multi-TB transfers.

    PS It is slow to/from 5400 SATA II drives.
  7. Your seagate drive is a 5400rpm drive and 130mb/s isn't bad at all. Its not the speed of the usb thats limiting your transfer speed, its the slow mechanical drive.

    Paulo - your usb3 speed may not be what you think it is. It all depends on how it was implemented on the motherbd and what chip was used. Some are as slow as usb2. Please try to find a review first.
    I'm also voting for the internal sata2 ssd. I have 2 home theatre systems. On in the living room with a triple core amd/8gbram/ samsung 830 128gb sata3 SSD that gets 450mb/s read speeds. One the the bedroom is an old intel dual core, 4gb ram, 64gb patriot pyro ssd on sata2 port and scores 240mb/s. Both have identical software loaded except for drivers. The bedroom pc is just as quick as the living room pc.
    Its not about the max read & write speeds. Its all about the random read and writes and in that respect SSD's cant outperform sata2 yet.
  8. After some decision, I decided to go for the usb3 solution, it's just much easier.
    The benchmarks show what you all said, it's not near the advertised speeds for the drive, but it's still an SSD and compared to the internal HDD is much much faster.
    So in the end, if you want performance, I agree, the only choice is an internal sata drive, but the ease of usb and the fact that an ssd is always much faster than a magnetic drive also make an external system drive a very good choice.
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