What prevents Theoretical Max speeds of an SSD using SATA 6 and/or USB 3?

I have a Crucial M4 256GB SSD in my laptop. The laptop has SATA 6 capability. When I run crystalMark on it though, I dont get anywhere near the max of Sata 6 max ability ( theoritically above 600Mb/s).

Likewise, with my M4 in a usb 3 external case ( OYEN Digital MiniPro - which has a Sata 6 capiable chipset) I dont get anywhere near the USB 3.0 Theoretical limit ( about 500Mb/s i think)

Im aware there will be some "overhead" to reduce speeds down a little but my questions are:

1. what are these overheads?
2. why is the reduction in speed so sevre?

In below image, my USB 3 SSD Crystal Mark result is the top image & my internal SSD is the bottom Crystal Mark Result.

Thanks!

 

USB3 is a lot less efficient than SATA. I think real-world speeds are just around half of theoretical. As for SATA III 6Gb/s, it appears to top out at around 500-550MB/s which isn't bad at all, particularly when compared to USB3. Your Crucial m4 is actually the bottleneck on SATA3. I believe the Samsung 840 Pro is capable of ~500MB/s in both sequential read and write. Personally don't think it's worth the current asking price, though.

 

SATA: Your SSD is not fast enough to saturate the bus. The Crucial M4 is 1.5 year old tech, after all...

USB: What you're seeing is pretty much the extent of what USB 3.0 can do, at least when using the default USB data transfer protocol. If your laptop supports either UASP or a proprietary file transfer protocol, you could potentially get higher speeds.

 

like the others said, your internal speeds are fine.

remember the concept of bottlenecks though. in a drive-to-drive transfer where the M4 is the destination, there are 3 potential bottlenecks: clearly, SATA 3 is not the bottleneck for write speeds, therefore, unless the source drive can read at more than 200MBs per second, it will be the bottleneck, not your M4. conversely, if the M4 is the source drive, your target drive must write at >400MB/s or it will be the bottleneck.

 

In short, replace all your drives with a Samsung 840 Pro 256/512GB. That way, SATA 3 becomes the bottleneck.

 

Thanks for the info guys.

Ive been running more tests, and at 4k random read, it seems like im actually being limited by USB3.

I ran a test, Random Read at 4k, with variying queue depth
Internal I can get a max of just over 40,000 IOPS, which translates to about 170mb/s
With USB3 I can get a max of just over 4,000 IOPS, translating to less than 20mb/s

At 4k it seems im limited by the IOPS that can be pushed through USB 3, although i cannot find any information on if there is a limit on the IOPS for USB 3.

 

What you are discovering is that USB X.XX any version is horrible for storage subsystem use.

In order of worst to best:

USB
FireWire
eSATA
Internal SATA
Intel Thunderbolt (when you really need SSD's RAID'ed for RED (4K) RAW video transfers/editing).

 

Id like to find out why though! such as if the USB 3 specification detailed a max IO limit assuming optimal block size.

 

USB was designed to work with anything and because of that the controller on the device has to encode the data to transfer over the usb cable. Once it reachs the mother board another controller or chipset decodes the data so your computer can understand the data. USB will tax your system a lot more. As in taxing the decoder aka chipsets as well as Cpu to translate the data. This is why you get different speeds that can very a decent amount on different motherboards. Sata is also designed to only receive/send a certain type of data and was primaryly designed for hard drives. Where usb was designed to receive a lot of different types of data. hope that answers your question.

 

Part of the USB specs are to annoy the he** out of consumers than need greater than minimum performance from peripherals, even like mice and keyboards.

What is really lacking in USB with regards to storage subsystems; real-time concurrency with low overhead and no USB-SATA conversions. This will never happen (storage subsystems are being (slowly) moved to higher bandwidth interfaces (PCI-e) and to eventually being managed by the processor (on-die) as the ultimate goal with a direct to cpu/cache/memory data path as possible).

Need any other USB specs explained in plain English?