[CentOS] Re: IHC7 RAID-1 or Kernel Software RAID-1?

[Scott Silva]

Feizhou spake the following on 7/18/2007 11:58 PM:
> Alvin Chang wrote:
>> On 18/07/07, Tony Mountifield
>> <tony at softins.clara.co.uk> wrote:
>>> In article <f7iufv$1cc$1 at softins.clara.co.uk>,
>>> Tony Mountifield
>>> <tony at softins.clara.co.uk> wrote:
>>> >
>>> > My question is: which kind of configuration will generally give me
>>> better
>>> > performance? To use the IHC7 RAID-1 as currently set up, or to use
>>> Linux
>>> > software RAID-1 as I am used to doing? Any other reasons to choose one
>>> > over the other?
>>>
>>> Thanks for the responses, confirming what I thought: disable SATA
>>> RAID and
>>> use Linux software RAID for mirroring. So that's what I've done.
>>>
>>> It appears that my Centos 4.4 install didn't know about dmraid
>>> devices anyway.
>> I personally would give fakeraid a because the hardware chipset
>> wouldn't take as much CPU time as soft-raid. Why are you using 4.4
>> instead of 4.5 as you mentioned in your previous post?
>>
> 
> There is a reason it is called FAKEraid. They provide zero cpu
> offloading, they do not come with a chip that does raid processing let
> alone a battery backed up write cache. The chipset only handles SATA or
> ATA channels.
> 
> Oh, if you want to try the hardware raid is faster than software raid
> line, then I have got news for you. Some time back, there was this i960
> chip from Intel that was very popular on hardware raid solutions. It
> sucked. It sucked big time. Yes, it did offload a fair bit of cpu
> processing from the AMD/Intel cpus then but the i960 was so slow, using
> software raid was just a no brainer since you get twice the speed for a
> 10% cpu load.
> 
> Today, hardware raid come with big memory caches and that is the only
> reason they are faster than software raid in certain cases like raid5.
> Any hardware raid card that does not come with a memory cache is not
> likely to be much faster than a software raid solution especially when
> using the more complicated raid arrays like raid5/6. You will notice
> that products from 3ware and Areca all now come with memory caches.
> There is no such thing as a cheap hardware raid card.
The i960 doesn't count, since it hasn't been used for a while. I think it was
designed as a printer rendering engine processor, and was never designed for
the load that raid imposed.

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