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Thread: USB Speeds from memory card transfer to PC

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    Ausphotography Regular wideangle's Avatar
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    USB Speeds from memory card transfer to PC

    Can anyone clarify if I am correct in saying this memory card when copying images to a PC via USB 3 could only manage maximum theoretical copy speed of 60MB/SEC? For the record I get around 40MB second speeds on this card transferring from the card reader to an internal HDD, if I transfer to an SSD the speed is around Would the limitation of the write speed to a PC be the card speed itself, because I imagine that USB 3 card reader can read/write much faster than this? The card reader being used is this one >http://www.lexar.com/node/4577

    Speeds from card reader to PC:

    via USB 2 to HDD - approx 27mb/second then drops with longer writes.
    via USB 3 to HDD OR SSD - approx 40mb/second
    Last edited by wideangle; 13-01-2014 at 4:48pm.
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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Wides. AFAIK/CT 60 MB/sec is the highest (theoretical) read speed for such cards. (I have two Sandisk CFs of this ilk.)
    The rest is up to the system used. The SSD would sure help in getting close to this.

    I also have two USB 3 HDDs, but alas, no USB3 on MB.
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    Quote Originally Posted by ameerat42 View Post
    Wides. AFAIK/CT 60 MB/sec is the highest (theoretical) read speed for such cards. (I have two Sandisk CFs of this ilk.)
    The rest is up to the system used. The SSD would sure help in getting close to this.

    I also have two USB 3 HDDs, but alas, no USB3 on MB.
    Am.
    I've found very little difference in relation to the transfer rate of this card onto a HDD or a SSD, pretty much the same speed via USB port - around 40mb second.

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    Yep, it is theoretical. You need USB3 connection, USB3 on motherboard, card that is capable of USB3 speeds. Every step, bit of gear in the path from card to SSD, every cable etc, needs to be able to transmit data at the max rate to achieve this.
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    Quote Originally Posted by wideangle View Post
    Can anyone clarify if I am correct in saying this memory card when copying images to a PC via USB 3 could only manage maximum theoretical copy speed of 60MB/SEC? For the record I get around 40MB second speeds on this card transferring from the card reader to an internal HDD, if I transfer to an SSD the speed is around Would the limitation of the write speed to a PC be the card speed itself, because I imagine that USB 3 card reader can read/write much faster than this? The card reader being used is this one >http://www.lexar.com/node/4577

    Speeds from card reader to PC:

    via USB 2 to HDD - approx 27mb/second then drops with longer writes.
    via USB 3 to HDD OR SSD - approx 40mb/second
    There are a few factors here at play.

    To get the easy stuff out of the way, USB 2.0 has a signalling rate of 480mbps, which translates to an effective theoretical data transfer rate of 35MBps. Add USB protocol overheads (bandwidth allocation etc) and latencies in controllers and software stacks, and your real-world rates fall to 20-30MBps - so 27 is right up there. IOW, USB 2.0 is the limiting factor.

    USB 3.0, OTOH, can easily achieve the 60MB/s stated on the card's 'specifications'. So we know that's not the bottleneck.

    Now for the moment, let's forget the card and look at the other end - writing to the [solid state] hard disk. The modern hard disk interface - eg. SATA - is far and away faster than the card or any disk (SSD or not) attached to it. So we can eliminate the interface as the bottleneck. Modern rotating hard disks are capable of sustaining media writes well above the 60MB/s, and you'd have to have a pretty badly fragmented disk to have write performance fall well below that. Solid state drives are faster again (and are not affected by fragmentation), so we can rule out your HDD/SSD device as the bottleneck.

    That leaves us with the card. The 'specification' (and I use the term loosely) states a 'maximum read/write transfer rate' of 60MB/s. This does not mean it can sustain that rate indefinitely. In fact, it specifically states that the sustained write rate is actually 20MB/s. Thus 60MB/s writes consist of bursts into the card's cache (and not the flash memory), and any transfers larger than the cache size would start to slow dramatically. As for read speeds - it's not explicitly specified. Probably because no-one really cares all that much; as long as you can stream video to the camera's LCD anything above that is not 'important'. It would seem that empirical evidence (yours) reveals that the sustained read rate of the card itself is actually 40MB/s.

    IOW, you're not going to get anything more out of the card, regardless of your equipment, because your equipment is (likely) already faster!
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    A royal pain in the bum! arthurking83's Avatar
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    My experiences:
    I have faster rated cards that perform slower when connected via the PC.

    I have an old 600x 8Gb CF card that can read and write faster than does my 1000x CF card using the same hardware on the PC.
    Problem is I can't confirm the performance of the old 600x card on the D800, where it gets tested more strenuously as the D800 doesn't recognize it.

    So (as per Galbraith's card performance review) the rated speed of the card is not only theoretical, but also dependent on the hardware used for the performance testing!
    That is, you could see a situation where a Sandisk 90Mb/s card, could in fact read and write more slowly than a Lexar 45Mb/s card when inserted into a Nikon D#
    But the performances may be reversed if used in a Canon #D camera.

    Also! The chip for the USB bus used by the manufacturer of your devices, both the chip on the USB controller on the PC and the controller in the USB3 card reader may be at odds with some of the overheads that tcdev comments on.

    That is, your card reader may be the bottle neck, your USB host controller chip may be the bottle neck, or the two communicating between themselves may be the issue.

    I have a myriad of USB3 devices, some work at speeds up to 75Mb/s others a wee bit slower, and one specifically useless device can't seem to hold a connection for more than a few gigabytes!(so it has to be connected to the USB 2 port for it to work).

    Unless you're willing to spend weeks testing various alternative arrangements, finding the issue is difficult if not impossible.

    FWIW: I have the exact same card reader, connected on USB3 which is controlled by a Renesas USB3 controller chip.
    With the 800x Lexar 32G CF card, I can get about 40Mb/s sustained write speeds, and about 60Mb/s read speeds.
    With the Patriot 600x 8G CF card(which doesn't work in the D800!), on the PC I see 60Mb/s write speeds, and anywhere between 40 and 70Mb/s read speeds(wide variance is dependent on files being transferred).
    Either way I see it, the slower card is (usually)faster, at least on the PC.

    On the D300, they feel about the same .. ie, too hard to differentiate any differences.


    Another experience: I know USB3 has at least up to 100Mb/s transfer capability.... probably more like 120Mb/s as I have a fast USB3 3T drive made from a Seagate HDD and a USB3 enclosure.
    I see over 100Mb/s sustained from this drive over hundreds of Gigs of photos, and I while see initial burst of over 200Mb/s .. I get about 120Mb/s for a few minutes until it eventually slows and settles to speeds more like 100Mb/s.
    Another USB3 device I have is a docking station. Bloody useless device that it is. It can see about 80 or so Mb/s for a few minutes .. once it reaches about (usually) 50Gigs transferred, it suddenly dies. Transfers stop for no reason other than the communication between it's controller chip and the mainboards USB3 chip goes AWOL!
    Many attempts to rectify this annoyance just lead to more frustration, so the only way to operate this(so called) USB3 device is on the old USB2 pipeline. The two USB3 chips in this chain are simply not fully compatible.

    So, as tcdev said, there are many factors at play here, and once you've understood them, you also have device compatibility to deal with too.

    BTW 40Mb/s is quite good.
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    Quote Originally Posted by arthurking83 View Post
    My experiences:
    I have faster rated cards that perform slower when connected via the PC.
    (snip)
    Many attempts to rectify this annoyance just lead to more frustration, so the only way to operate this(so called) USB3 device is on the old USB2 pipeline. The two USB3 chips in this chain are simply not fully compatible.
    (snip)
    So, as tcdev said, there are many factors at play here, and once you've understood them, you also have device compatibility to deal with too.
    USB has been notoriously poorly implemented right from the beginning, from the bodgy software stacks in Windows to the controller chips that suddenly go AWOL for no reason. The history of SD cards isn't much better, from cards that aren't recognised in some devices, to faulty flash devices. Now add those two track records together and you can see what a mine-field it can be trying to get reliable USB transfer and storage!

    Just yesterday my SD card suddenly 'disappeared' from my PC mid-transfer and refused to be recognised again until I switched card readers. I've had problems with my D90 cards not being recognised in various PC's before, and I only use genuine Sandisk Ultra cards.

    So for me, I'm happy just to see the transfer complete without errors! Whether it's 120, 60 or even 40MB/s, I don't care!

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    A royal pain in the bum! arthurking83's Avatar
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    Quote Originally Posted by tcdev View Post
    ......
    So for me, I'm happy just to see the transfer complete without errors! Whether it's 120, 60 or even 40MB/s, I don't care!
    LOL .. you and me both!

    This thread got me interested in my issue with this annoying USB3(yeah! right!!) docking station I have.

    From day one it caused me no end of grief in trying to backup data to bare drives(which get stored) .. and on drives I use for various media .. streaming and stuff.

    Ended up searching for more info about it .. on and off, and only just the other day, I thought to try again, and bingo!


    whoot!

    I found a new firmware for the chipset(on the docking station) and thought .. yeah, try again.

    Was a bit dubious tho as to the way the firmware was being loaded into the docking station, the program used looked dodgy for some reason.
    But the firmware kind of looked legit.

    Anyhow .. long story short, and finally some love!

    Got this damned USB3 dock working via USB3 now, with only one small niggle in that everytime Windows starts, the two drives that reside in there semi permanently always come up with the annoying autoplay dialogue box.

    Transferred nearly 2Tb of files from an external USB3 drive to a(slow-ish .. green!) 3Tb drive last weekend, and it seemed to sustain over 40Mb/s write speed.
    More importantly .. 40Mb/s over the whole 1.8Tb's of data.
    Left it running overnight and came back in the morning bleary eyed .. wondering did anything work .. did it stop short.

    Verified and now working.


    I got a Sandisk 4Gb UltraII CF currently sitting on my desk. Not recognised in the D70s any more .. Windows wants to fix errors on it, D800 sees it OK tho ....

    I've got this feeling there's another about to go in the bin!

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