[mythtv-users] Should I use LVM on this new raid?

Brian Foddy bfoddy at visi.com
Sat Sep 22 03:53:33 UTC 2007

On Friday 21 September 2007, Chad wrote:

> As others have mentioned, it's usually an either/or thing.  There
> isn't any obvious benefit (that I can see with these internet blinders
> :D) to running an LVM ontop of a RAID.  Your RAID will perform the
> disk aggregation that you may be thinking you want LVM to do.  The
> more disks you throw into your array, the larger raid0 gets, not
> multiple "disks" as seen by your OS since your RAID card is taking
> care of that end.
> On the filesystem end, XFS seems like a good option.  IIRC it's
> (current) upper filesize limit is 16TB (that's per file).  So for now,
> I don't see that being a problem with anything currently available
> (even if you string together all 6 Star Wars in 1080p I don't think
> you'd hit 16TB).  Also moving from raid0 to raid5 might require you to
> wipe the data (depends on the card and as other's have mentioned, seem
> to be some that can, seems like it's probably a software option
> though, not part of the RAID controller config) so you may want to
> choose your RAID configuration now.  And as someone may point out
> (with a link to the anti-raid page), most home users will not benefit
> from raid5, so go for the gusto! if you ask me, raid0 that thing and
> take it out to it's max 8 ports and store some of my stuff ;)

Several good replies quickly, so I'll try and reply in a generic way.
The 3ware 9650-8 is already here; picked it off ebay last week
at a decent price, but still kinda pricey ($400) but I hope
worth it.  The Linux support seems very good, that's
the big reason I opted for the more expensive 3ware card.

According to the all the manuals I've seen, it will allow me to 
add disks to an existing RAID unit dynamically, growing the unit in size, 
and/or reformatting the unit from one raid type to another 
(with some obvious limitations that require additional disks or 
other non-sensical combos); all without the host seeing any changes
or having to reformat the fs; provided the fs can be expanded.  
I only have 2 disks to start with so I will see soon.

I'm leaning towards using LVM on top of the hardware raid,
maybe make the raid card divide its space into 1TB chunks, each
with the overall raid support of the card.  Then
using the LVM to manage those chunks into filesystem space.
That way if I want to make smaller space for other filesystems
I can do it easily.  I think I'll play around with things for a day
or 2 before making any permanent decisions.  Right now I
just have theory, manuals, and others as experience.


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