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

Chad masterclc at gmail.com
Sat Sep 22 03:31:33 UTC 2007

On 9/21/07, Brian Foddy <bfoddy at visi.com> wrote:
> Building a new mammoth backend server.  It has a
> 3ware 9650 8port raid card, and I'm starting out with
> 2 x 1000GB HDs, initially I plan them in raid0.  As
> the budget will allow I'll probably add a couple more
> and go to raid5.  I won't guess how many total drives
> it might grow to, probably 4-5 in a raid5 setup.  And
> starting with 1000GB drives pretty much locks me into
> that size forever.
> As I get acquainted with the raid card, it has pretty
> easy support for adding  new drives to the raid without
> reformatting.
> In addition to the videos, the raid will also hold other
> bulky backups, mirrors of internet dirs, and other misc
> storage as needed, but predominately video.
> Would people suggest I add LVM software on top of this,
> or will I have enough flexibility with just the raid?  Also,
> I've normally used XFS, but with LVM the inability to
> shrink a filesystem gives me pause about using it.
> I've always had good luck with XFS tho, and really like its
> deletion speed.  Question to myself, would I ever need to
> shrink the video filesystem?
> A multi-TB filesystem isn't something that is easy to
> backup and reformat...
> Thanks,
> Brian
> _______________________________________________

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 ;)


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