On Dec 20, 2007 11:10 AM, Tracy R Reed <[EMAIL PROTECTED]> wrote:
> Dexter Filmore wrote:
> > ZFS is software. Don't know how ZFS performs, but being software I *bet* it
> > won't write 400MB/s like a hardware controller does. (Ok, 400 at a
> > sufficient
> > high disk number, 6 or 8). I got soft raid 5 on my server and besides that
> > it
> > is troublesome in terms of stability (had at least 6 occurances where a disk
> > flew from the array for no apparent reason, disk checks turned out disk was
> > fine so I re-added it each time) it does little more then 10MB/s writes at
> > cost of many cpu cycles.
>
> Your first statement makes no sense. That hardware controller runs
> software too. There is no such thing as "hardware is better than
> software" or vice versa. They are apples and oranges. You cannot have
> one without the other. And RAID 5 sucks in general for performance. On a
> P4 system, XOR computation can be performed by the MMX unit
> (independently of the main cpu) at 2Gbytes/sec, well above the needs of
> I/O systems. So the RAID calculations themselves aren't likely to be
> causing noticeable CPU performance differences.
Yeh, I think the point is that the "hardware" being used in a
software RAID i.e. the "main" cpu (commodity) is running closer
to Moore's Law than the "hardware" in a disk controller so the
"hardware" used by a "software" RAID is faster.
This is kind of hard to say, so let me try again.
There is only "firmware" = "hardware" + "software" to do some task.
So we consider two cases:
1) "main" => f0 = h0 + s0
2) "disk ctrl" => f1 = h1 + s1
Assertion: because of manufacturing economics the "main" cpus will
always be running closer to Moore's Law than are disk controllers.
So unless their is some serious architectural issue there is
_no_ advantage to using the "disk ctrl" to run the software.
Moreover there is a cost and performance disadvantage for so
doing.
BobLQ
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