Re: Moving from RAID 0 to LVM RAID?

["Matthew Gillen" <user=50@nabble.blu.org>]

 Scott R. Ehrlich wrote: 
> When I get a replacement disk and build the system from the ground up 
> again, I could, conceivably, use hardware RAID 1 for the OS on two 
> disks, and CentOS 5 64-bit's LVM for software RAID 5 (or maybe 1+0 if 
> available) on the remaining for 4 disks, maybe 3 disks as active and the 
> 4th as a hot spare? 
> 
> I've never had much faith in software raid, since it is not 
> hardware-based, and there would be a performance hit, but in this case, 
> it could be an option. 

 From a purely logical standpoint (I don't have the inclination to do actual 
performance tests myself, since I don't have any RAID hardware, and the 
software works fine for me), there's not much that hardware will gain you 
over software when doing RAID-1.  RAID-1 is all about bandwidth to the 
drives, so as long as you have separate buses that can write to more than 
one disk in parallel, that probably dwarfs any other issues. 

With RAID-5 the story is a little different, since the parity calculation 
would actually chew up some CPU cycles.  There, hardware-assist would 
probably make a noticeable difference.  Personally, I don't see the 
attraction to RAID-5; it's more complexity for very marginal cost benefit 
(which is probably negated completely by the cost of the RAID controller...) 

I'd be curious to see some performance tests of a hardware RAID controller 
vs. a couple SATA drives using SW RAID, for both the 1 and 5 flavors. 

Finally, one last point in favor of SW RAID: a bug in the implementation can 
  be fixed easily.  If your RAID-controller has a bug, you're fsck'd. 

Matt 

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