[mythtv-users] OT Hardware RAID 5 non-Recommendations

Steven Adeff adeffs.mythtv at gmail.com
Wed Dec 20 20:56:11 UTC 2006

On 12/20/06, Brad Templeton <brad+myth at templetons.com> wrote:
> On Tue, Dec 19, 2006 at 07:27:25PM -0500, Steven Adeff wrote:
> > > because slower disks (ie. 4200 rpm) are quieter, generate
> > > less heat and fail less frequently.   Though you can hardly
> > > get such slow spinning disks any more.
> > >
> > > When it comes to Myth, raid does one thing for you -- protect
> > > you from single hard disk failures.   A better fan will
> > > do quite a bit of that, too.
> >
> > it does with 3 HD tuners and a pvr-150 and two HD capable frontends,
> > all able to record and playback at the same time with commflagging,
> > *because* your running RAID.
> So that's at most 100 megabits.  (The comflagging is niced and does
> not have real-time needs.)   You have found an ordinary disk
> to be incapable of handling that load?  It's a very slow, predictable
> load, read in the same order it was written.

not even close. I could barely get 1 HD 1 PVR-150 and 1 HD playback
with my original RAID5 setup, I since went to a RAID 10 with 4 drives
and its finally capable of handling all that along with my SQL
database. I'm looking to add two more drives, at which point I think I
can go back to RAID5 and still get the speed I need and gain a lot of
extra space (which would be *lovely*.

> This is, to me, a very extreme need, but I would be curious if it
> could not be met by a single disk, or at least a single video disk
> with the OS files (which are accessed at random) on a different one.

the problem is that, the more you record the more your HDD head has to
move around, and the more you read the more your head has to do double
duty. So while in theory one solid stream at said bitrate may work, in
actuality its 5, 6, 7 etc different operations. As well, writing takes
longer than reading, so now you've got timing issues.

> I have always been curious about folks with giant setups.  I have
> one HD tuner and on SD tuner and they are rarely on at the same
> time, and I've had one HD conflict in a couple of years.  Mind
> you, I view conflicts as god's way of telling me I watch too
> much TV.    I view Myth as something that presents me with too
> many choices of what to watch, and its ease diminishes the
> number of DVDs I watch, even though they are higher quality
> programming and image (over SDTV) that I just can't fathom wanting
> even more.   Or wanting it for children.

Occasionally there are three things on network TV I, my apt-mate, or a
friend watch. I've even had it occur where five things came up (one
had to be relegated to the PVR in that case). Sadly the HD tuners can
only get OTA stuff, so the PVR records a lot. Plus theres a good
amount of filler, sports, etc. that don't necessarily get watched, but
its easier to record all the games than have to worry if I remembered
to set one to record.

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