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Have a 4-disk RAID 5 array of 250Gig HDs that I am looking to use for performing video capture and editing. Two of the disks are internal, and two are ...
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  1. #1
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    USB2 doesn't keep up with capture under 2.4.27


    Have a 4-disk RAID 5 array of 250Gig HDs that I am looking to use for performing video capture and editing. Two of the disks are internal, and two are external and connected using a USB2 card. Running under a Debian installation with a 2.4.27 kernel, I can capture for a few minutes, but then I start to drop frames, and the percentage dropped gets worse as time goes on.

    Would going to a 2.6 kernel where I gather there are some additional features available "fix" this, or do I need to look at moving to firewire or something else? I'm reticent to move to firewire as I was having troubles with my system "forgetting" that it could talk to some of the disks after a reboot using firewire enclosures, but if I have to then I guess I have to

    Thanks,
    Ewan

  2. #2
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    If you are doing any video capture I would strongly suggest firewire. USB 2.0 is faster than firewire'a' however the transfer of video is much faster using firewire.

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    Understand that firewire is preferable, that's why the capture device itself is on my firewire bus.

    However, at least in the distributions I've tried, firewire support is somewhat shaky when it comes to external hard drives. Which is why I was looking at USB2. I haven't had one occasion where the system boots up not being able to see both drives, and even when it's dropping frames I don't lose a HD as would sometimes happen with firewire. It may be the firewire enclosure I was using were the problem, but that gets to be a bit of an expensive experiment to go through several of those.

    Would another option be to get a second USB2 card? Then I'd only have one drive on each card, which "should" improve throughput - unless you're saying that the load on the CPU to drive a USB2 device is the actual limiting factor?

    TIA,
    Ewan

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  5. #4
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    Using a USB 2.0 card is better than using on-board USB because the processes are preformed more by the CPU. A card will split if not handle all the request given by the CPU. A second might boost some but I doubt you will see any gain at all.

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    Well, I got my answer by using a second card and moving to kernel 2.6.7 - sort of.

    Put in the second card, and it showed up in usbview, but the disk attached to it showed up as being attached to an "unknown" usb hub at only 1.1 speed.

    Figured this might be a 2.4 kernel issue (with USB), and so rebooted into kernel 2.6.7. Nope, the second card still showed up "funny". However I had somehow convinced it to load ehci-hcd (had not been able to do that before) and so the first disk was running at Hi Speed.

    Just for grins I pulled the second drive off the second card, and plugged it back into the first card. Now both disks were showing hi speed.

    Having read that the USB drivers for kernel 2.6 were more "efficient", I decided to see what would happen. Sure enough, I can now capture (at least 10 minutes) without a single dropped frame.

    So, adding a second card evidently did "fix" the problem, just not directly

    FWIW,
    Ewan

  7. #6
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    thats nice

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