[mythtv-users] LVM2 Striping Suggestions...

Richard Freeman r-mythtv at thefreemanclan.net
Sun Sep 24 11:10:30 UTC 2006

Andy Speagle wrote:
> let me get your opinion of how well this system will function.

I think you'll be fine - my hardware is fairly similar (64-bit, but if
anything you'll have more stability and not much less performance for
something like streaming video).  I can easily record two SD and one HD
stream at once, and I don't have any kind of RAID (just a hodge-podge of
linear LVM2 partitions across a couple of drives).

Keep in mind that SD streams are typically only recorded at 1Mbps.
ATA-100 is 100Mbps (go figure).  Now, head thrashing is going to greatly
reduce throughput if you are recording 40 streams at once, but for even
a dozen streams you're probably OK as long as you have decent RAM for
buffering.  Your typical Tivo probably has only a few MB of RAM, a
really cheap CPU (with hardware MPEG-codecs) and a 5400-RPM drive - so
it isn't like you need a lot of raw horsepower.

The biggest thing I have to be mindful of is not overdoing it with other
tasks on the backend - I tend to tinker a lot so I schedule backend jobs
to not run at hours I would be interactively using the computer.  If
you're just checking email, browsing the web, and typing papers you
won't have issues.  On the other hand if you're running 3D games while
building 15 packages on gentoo while your family is browsing your photo
gallery hosted on apache on your backend while recording two shows while
the family in the living room is streaming another you might start to
get lost frames in your recordings.  If you have a dedicated myth box
you probably don't even have to worry about stuff like that.

Honestly, given your set of hardware I'd personally just go with a
linear LVM2 configuration - that uses all your disk space and easily
lets you add more.  If the only thing on those drives is your video
directory then having redundancy only matters if you REALLY don't want
to lose your shows.  If a drive failed you could have the other drive up
and running in 5 minutes and it wouldn't require setting everything up
all over again - and a few days later you could add another drive and be
at full capacity (if you aren't using RAID it is trivial to add more
space using LVM2 and xfs).  Now, everything else on your system (other
than your video directory) is a different story - I'd back that up or
RAID it to avoid having to spend hours reconfiguring your system.

Now, if you do literally stay 3 seasons behind in catching up with your
TV and don't want to lose 300 hours of stuff you haven't seen if a drive
fails, then perhaps RAID is the way to go with your video partition.

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