Tracy R Reed wrote:
Has anyone taken a look at the cpu's on their hardware RAID controllers?
3Ware's stuff runs at 66Mhz. But it's not an x86 cpu so I'm not sure
how it compares. If we figure that the most cpu power we could possibly
waste by doing it in software is limited to the cpu power of the
hardware RAID controller how much are we really wasting?
And 3Ware (last I checked) had a dedicated chip which did all the RAID 5
XOR processing so it never hit any of the systems buses.
Do *not* underestimate the amount of power it takes to do that. The big
problem with software RAID 5 is that you have to move the data from all
the disks into your memory, have the CPU chew on it all to produce the
XOR stripe, and then move it all back.
This does several things:
A) It saturates your internal PCI bus
B) It saturates your processor because the calculations are pure XOR
C) It displaces good cache information with something used only once
Now, if you are creating a dedicated file server fed by a single
1000BaseT with a 3GHz Xeon/Opteron and a PCI-E/X interface, you could
care less. Everything internally is so overpowered that it doesn't
matter and the external interface is so slow that you can't affect things.
A more modest server fed with more and faster network interfaces will
start getting conflicts. Also, a standard PCI bus will get saturated
with even a couple of spindles.
It's not always about the CPU.
-a
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