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

Feizhou feizhou at graffiti.net
Thu Jul 19 06:58:40 UTC 2007

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.

More information about the CentOS mailing list