[NCLUG] USB 3.0 PCI cards

[Sean Reifschneider]

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On 07/06/2011 04:48 PM, Bill Thorson wrote:
> backup devices.  I am currently using them on USB 2.0 because I have
> no hardware with 3.0 ports.  I'd sure like to speed this up.  This

First of all, are you sure that USB 2.0 is your bottleneck here?  I'm sure
these drives can more than saturate USB 2.0 when streaming large files, but
for backups it often involves many files and a lot of seeking...  For
example, I have a backup system with 4 3TB drives connected up directly via
SATA, and during my backups I get around 3-4MB/sec of raw throughput on the
discs, sometimes spiking up to 10MB/sec.

The drives I'm talking about are slower, 5400-ish RPM rather than 7200RPM
to reduce power usage.  But I also have 8GB of RAM and a 32GB SSD as a
level-2 meta-data cache to reduce seeking, and even with that I'm getting
60+% utilization at 3-10MB/sec.

So, use tools like "iostat -x5" and "vmstat 5" to see how hard the discs
are actually getting hit.  The MB/sec rate I'm quoting is coming from the
ZFS tools, I think you can get them out of iostat, but I think you have to
calculate them out of the stats you get from iostat.

So, before you start down the path of new hardware compatibility, make sure
that you're spending on the bottleneck.

>    say with their card you will only get up to 2x USB 2.0.  Is this
>    a function of the card, PCI or both?  Can I find better that will

If this is actually a PCI card, not PCI Express, then it's likely a
limitation of PCI; normal PCI will do ~100MBsec, or around 2x USB 2.0...
If it's PCI-Express, it depends on the number of lanes the card has, but
even a 1x PCI Express 1.x card has 250MB/sec of bandwidth.  v3.x has
1GB/sec per lane...  So PCI-X or PCI Express are the way you want to go for
bandwidth reasons...

Have you considered going ESATA?  If you have free SATA ports on the
motherboard, ESATA can be done with just a cable I believe, or ESATA cards
are cheap and well supported under Linux -- definitely more "mature" than
I'd expect USB 3.0 to be.   But I don't honestly know how well supported
USB 3.0 is.

Sean
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