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

Brad Templeton brad+myth at templetons.com
Tue Dec 19 01:01:23 UTC 2006

On Mon, Dec 18, 2006 at 08:47:33AM -0500, Steven Adeff wrote:
> On 12/17/06, Brad Templeton <brad+myth at templetons.com> wrote:
> > It is also worth considering not doing RAID at all.   Seriously.
> > Yes, drives are failing more often -- though if you keep them cool,
> > that improves a great deal.   Of course, keeping them cool requires
> > fans you may not want in your living room.    I believe you can get
> > a box that goes in your 5.25" bay zone in larger cases with a 120mm
> > fan, you can certainly get 92mm fans for such boxes.
> >
> > If it's a backend, not in the living room, put in the big, slow fans
> > for good airflow and low noise.
> >
> > RAID as a backup protects you from drive failure, but it does not
> > protect you from the far more common cause of loss, which is
> > accidental deletion.   It also doesn't protect against the house
> > burning down or similar troubles.
> >
> > You may consider that videos are not as much in need of backup
> > and that you would rather than 1.5x or 2x the storage than have
> > backup.   Videos can often be recovered over time (shows get run
> > again) or for those inclined, there are sources on the net where
> > you might question the ethics of using them for obtaining videos,
> > but not for recoving ones you legitimately had.
> >
> > However, barring that, you may want to consider that
> > extra drives (as needed for RAID 5) require extra power, heat and
> > noise.  About 10w for a typical drive, which here means $10 per
> > year or $30 over the 3 year life of a drive.     Thus a 750mb
> > drive may be cheaper than two 400gb drives over time.  Not
> > counting the fancy controller.
> RAID also gives you speed, which for folks with HDTV becomes
> important. So with RAID 5 you get a two-fer, speed and "reliability".
> (plus, what serious TV watcher doesn't do off-site backup of their
> myth recordings? ;-)

Speed is not important for HDTV.  Full bore 1080i HDTV is about
16 megabits/second.     Just about any disk you will get today
will read/write over 300 megabits/second for one disk.   (Yes, the
ATA and SATA busses are much faster than 300 megabits, but
the disks are not that fast.)

Truth is, for an HTPC, the slower the disk is, the better,
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.

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