Re: Moving from RAID 0 to LVM RAID?

["Ben Holland" <user=122@nabble.blu.org>]

 " Now, from the OS side, LVM is an option.   Say the RAID controller only 
allows hardware striping or mirroring for logical volumes, but I want to 
use more than two disks, and I don't want the RAID 0 problem again. 


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?" 

>From what I understand about LVM's it doesn't buy you anything and will make 
your headache only so much worse. If you have a computer that allows 3 
drives in it, chances are very high that it will have a raid 5 controller 
built in, if it doesn't you have several options. RAID 1 2 drives using 2 
other drives as backup, Software raid 5 3 drives using one as a hotspare, 
software raid 4 drives (this benefit is that you don't loose AS much disk 
space as the other 2). LVM doesn't buy you anything, sure you can group 
together volumes but if a drive dies, then you loose all the LVM's 
associated with it, this is bad and in fact your LVM controller may really 
hate you, I haven't had experience with LVM's and a disk from that group 
dieing, but i'm almost sure it's not pleasant. If you are seriously 
concerned about disk I/O this much it's worth it for you to invest in a san, 
more computers or the like IHMO. ~Ben 

On Thu, Mar 6, 2008 at 6:56 PM, Scott R. Ehrlich <[hidden email]> wrote: 

> So I've learned a valuable RAID 0 lesson, and it fortunately was not a 
> major catastrophy.  I got lucky, and had a workable-enough backup on tape 
> to make the user who needed some data happy. 
> 
> Now, from the OS side, LVM is an option.   Say the RAID controller only 
> allows hardware striping or mirroring for logical volumes, but I want to 
> use more than two disks, and I don't want the RAID 0 problem again. 
> 
> 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. 
> 
> Insights from the OS-created RAID experience welcome. 
> 
> Thanks again. 
> 
> Scott 
> 
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