[mythtv-users] 2 TB Hard Drive Recommendations

Brian Wood beww at beww.org
Mon Dec 6 14:59:49 UTC 2010

On Monday, December 06, 2010 07:40:32 am Jay Ashworth wrote:
> ----- Original Message -----
> > From: "Simon Hobson" <linux at thehobsons.co.uk>
> > 
> > Jean-Yves Avenard wrote:
> > >so two drives out of 6 dying in 18 months, so close to each other
> > >isn't that great.
> > 
> > That's one of the problems where the idea of RAID breaks down. You
> > buy a set of disks (same make and model, possibly even from the
> > same manufacturing batch), stuff them in an enclosure, and run
> > them for the same power on hours, doing the same usage profile -
> > ie they are run under near identical conditions. That means the
> > failures are liable to be less distributed temporally than you
> > might be thinking.
> > 
> > So you've massively increased the chance of two (or more)
> > simultaneous failures.
> > 
> > I saw that in one of our Unix servers at my last job. A drive
> > failed, and it took our maintainers a while to get a replacement
> > because they struggled to understand that they can't supply any
> > old "9GB drive" and it must be at least the same number of blocks
> > as the smallest in the array. By the time it did get replaced, two
> > more were showing an increasing error count and I think we
> > replaced 3 in an array of 4 ! For that reason, I've always setup
> > my arrays to use a bit less than the full disk to allow for a
> > slightly smaller drive as a replacement.
> <rant>
> If you buy *anything*, hard disks for a RAID, redundant power
> supplies, or what have you, where "pull a unit and replace it" is a
> fix...
> and you do not buy the spare unit at build time, test it, bag it, and
> stick it on a shelf, you're just fooling yourself.
> </rant>
> If you're really motivated about this, you can buy 6 drives for your
> RAID5, and rotate one in every 3 months.  That will spread your
> failures, too.

Also remember that no matter how good your RAID array is, it is *not* a 
backup solution. It's a system to minimize (not eliminate) problems 
caused by drive failures, it does not back up your data, or in any way 
protect you from accidentally rm-ing your data into oblivion.

Spreading the load among several drives can also improve both read and 
write performance.

Of course everyone knows all this, but too many people think RAID is the 
solution to data loss, which it isn't, only regular backups can do that.

But since Myth is only television, I wouldn't worry too much.

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