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

Joel Anderson joel at geekless.ca
Sat Sep 22 13:01:05 UTC 2007

On 9/21/07, Brian Foddy wrote:
> 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.
> Brian
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Hi Brian,

I've recently set up a similar card in my backend, a Promise EX8350
with 3 x 320GB in a raid5.  In general it performs quite well and as
with your card raid expansion should be possible in the future, so I
went with xfs directly on a raid5 ld.  I think having LVM in the mix
does add an additional level of flexibility, and debated the same
question.  It also ups the complexity, and so I opted for the more
straightforward setup.

Unfortunately, I am also experiencing random system lockups which I
have narrowed down to the card and/or it's drivers.  Promise has so
far been quite unhelpful, and has left me out in the cold without any
help even to determine if I require them to honour their warranty on
the hardware.  I used to be a fan of their products, but I definitely
don't recommend anyone buy this one.  Please share your 3ware
experience with the list once you've had some time to play.  I'm still
debating whether to go back to sw raid, and I'm sure others on the
list who are even thinking of using a similar hw solution would
appreciate the data point.

Joel Anderson

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