[Novalug] Disk Controllers

Maxwell Spangler maxlists@maxwellspangler.com
Wed Feb 23 22:48:04 EST 2011


On Wed, 2011-02-23 at 10:39 -0500, Dan Arico wrote:
> Can anyone make a hardware recommendation? The disk controller on my 
> motherboard has gone bad. I need a 4-port SATA controller that plugs into  
> PCIe.

SATA devices are 1.5 Gbps, 3.0 Gbps or 6.0 Gbps.  If you connect two 1.5
Gbps SATA devices and start reading from them, you may need 1.5 x 2 =
3.0 Gbps of bandwidth to the host.  A four port card supporting 3.0 Gbps
drives, for example, would theoretically need 4 x 3.0Gbps = 12 Gbps.

This is a challenge for consumers like you who wish to buy a cheap
multi-port card and pop it in your existing system.

On my HP desktop I have one 16-lane PCIe slot occupied by a PCIe
graphics card and four 1 lane PCIe slots available.

If they are PCIe 2.0 one of those 1-lane PCIe slots will provide 4 Gbps
of bandwidth allowing an add-in PCIe SATA card to support 2 SATA ports.

But in order to get 4 ports you'd need a four lane PCIe card which has
enough bandwidth to support four simultaneous SATA ports. Only higher
end motherboards and servers have these available.

The calculations you've seen above have caused manufacturers to produce
"fair" cost 2 port cards (for basic 1 lane PCIe slots) and rather
expensive four, six and eight port cards.  What the card can do and how
many ports it has simply reflects the market they expect will be using
it.

Motherboards with contemporary chipsets often have four to six SATA
ports and these are connected directly to the motherboard chipset for a
very fast, optimized connection.

So to some extent the other poster is correct in that instead of
spending $200 for a four port SATA card it might be cost effective to
replace the motherboard with a compatible model that has 4-6 ports built
into the motherboard.  Not a simple task, but something to consider if
you're up for it.

Hope this discussion interests those reading it.  It was an eye-opening
opportunity to learn this stuff.  Gone are the days of buying a fast PCI
UltraWide SCSI card, hooking up a bunch of drives and just being happy
about it. Things are too fast now.


-- 
Maxwell Spangler
========================================================================
        Linux System Administration / Computing Services
        Photography / Graphics Design / Writing
        Boulder, Colorado
        http://www.maxwellspangler.com
        




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