[mythtv-users] Fastest RAID for HD?

[David Brodbeck]

On Feb 14, 2008, at 10:00 AM, Brian Wood wrote:
> I would agree that under some circumstances (fast CPU, running on a  
> good
> UPS) Linux software RAID can be as good as some hardware RAID setups.

It also depends on the controller architecture.  If you're running  
software RAID on IDE, for example, and you have multiple drives on the  
same cable, performance will suffer.  This is especially true of RAID  
5 because of the write penalty.  Drives on the same cable can only be  
accessed sequentially, not in parallel.

I haven't used RAID 5 with MythTV.  It's likely more than good  
enough.  But for applications where performance is important the  
commercial world is mostly moving to RAID 0+1 or 1+0 (aka RAID 10),  
which has better write performance and more redundancy.  The downside,  
of course, is you need more drives, since you only get 50% of the  
total storage capacity.

Actually, I'd question whether RAID is really necessary for  MythTV.   
It depends on how upset you'd be if you lost some of your recordings.   
If the answer is "not very," it might make more sense to just use the  
drives as individual drives, and use storage groups to spread the  
recordings across them.  Believe it or not I've seen commercial CCTV  
DVR systems that took exactly this approach.  I would prefer this to  
RAID 0 or LVM striping, because if a drive fails in a RAID 0 array you  
might lose the whole filesystem, whereas if a drive fails using  
storage groups you just lose the recordings on that one drive.