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

Brad Templeton brad+myth at templetons.com
Fri Dec 22 22:37:38 UTC 2006

On Wed, Dec 20, 2006 at 03:56:11PM -0500, Steven Adeff wrote:
> > 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*.

There must be something wrong with your setup.   I, and many other
people here have perfectly working setups with perfectly ordinary
drives, doing HD and SD.   I even watch my HD remotely over the
100 megabit ethernet.    That does cause some problems with fast
forward of HD content -- it gets quite jerky, and 3x and 5x actually
run slower than that -- but that's the ethernet's fault not the disk's,
as if I watch on the real backend it's no trouble.

> 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.

Of course, but with reasonable buffering and read-ahead seeking should
be modeset and handleable.   As noted many people here do fine with
multiple tuner setups.
> 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.

Yes, that's a suitable use for a large setup.   Until we move to the
world of pick and choose download TV, one can imagine it would be a good
idea with cheap cards and disks to just record lots of stuff and delete
quickly if you want it.  I've even envisioned a world where you record
everything, and then wait for people to rate the programs, and delete anything
not on your regular watch list that does not get highly positive content.

On the other hand, we're getting very close to the world of download
on demand, which is perhaps a better way to handle it if we can convince
them not to go nuts on the drm.

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