[mythtv-users] Question re: available SATA ports and linux software RAID

[Robin Hill]

On Fri Apr 08, 2011 at 01:40:43PM -0400, Bobby Gill wrote:

> I have a question about PCI-E speed and what to do, I am thinking of either
> of these cards:
> 
> 1. http://www.newegg.com/Product/Product.aspx?Item=N82E16816132018 (RC-218)
> 2. http://www.newegg.com/Product/Product.aspx?Item=N82E16816132008 (RC-211)
> 
> Now if I get the RC-211 (2-port), it is limited to x1, but I could get 3 of
> them for the price of one RC-218 (4-port), but this latter one uses x4. So
> the cost comparison is fairly clear (1 4-port card same as 3 2-port cards),
> but what would the difference in speed be in using 3 cards in x1, vs. 1 card
> in x4??
> 
Well, a PCIe 2.0 x1 slot provides 500MB/s of bandwidth, and a single
SATA-2 drive can hit 300MB/s (though I'm not sure it sustains that - I
think that'll just be reading from cache). Anyway, that means 2 drives
can more than saturate the x1 card.  Of course, with 3 cards and 4
drives, you're only hitting that on 1 of them. 

The PCIe x4 slot correspondingly provides 2GB/s of bandwidth, and the 4
drives will max at 1.2GB/s, so there's bandwidth to spare there (though
I would've thought they'd go for 6 ports instead of just 4).

If you're only wanting the 4 drives, then I'd go with the RC-218.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <myth at robinhill.me.uk>  |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |
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