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LVM + RAID follow up

Derek Atkins wrote:
> Quoting Tom Metro:
>> RAID-1 is a no brainer, but what I wonder about is the use of higher 
>> order RAID or LVM layered on top of non-RAID volumes in the case of 
>> "budget" systems where you don't have backups (or at least frequent 
>> backups).
> It depends on your usage.  What are you storing on the system...

As noted, non-original video for a MythTV system. Thus the data is 
valuable, but not necessarily valuable enough to warrant doubling the 
storage costs.

> LVM is another way to accomplish RAID0, so I'd question
> whether you want a true RAID-0 vs. just using LVM.

I don't think that's the case. Both may have the side effect of creating 
a volume that spans multiple physical disks, but I believe only RAID 0 
actually uses striping to distribute the data across the physical disks.

In any case, this is tangential to the question.

> For myth video I'd just mount the disks separately and configure Myth
> to load-share the space across the mountpoints.  This way if you lose
> a drive you only lose the videos on that drive and not ALL your videos.

That's exactly the scenario I was wondering about, and that sounds like 
a vote against LVM for this application. I wasn't aware that MythTV had 
specific support for "load sharing" across multiple file systems (having 
not installed it yet). If so, that may eliminate much of the benefit to 
using LVM in this case.

I still may opt to setup the two data drives in a RAID 1 set initially, 
if that leaves me the option of breaking the set in the future when more 
space is needed, providing I can get away with reformatting one of the 
drives, and continuing to use the other drive as-is outside of the RAID 
set. Then I can defer until later the question of whether to buy 
more/bigger dives while maintaining mirroring, or simply adding more 
non-mirrored volumes.


Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
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