[mythtv-users] 2 TB Hard Drive Recommendations

Jay Ashworth jra at baylink.com
Mon Dec 6 17:42:21 UTC 2010

----- Original Message -----
> From: "Simon Hobson" <linux at thehobsons.co.uk>
> >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.
> There is one downside to that though - it means that each time you
> rotate a drive, you are deliberately downgrading your system (this
> was striped and mirrored for max performance with redundancy) AND you
> are exposing yourself for a time window to a drive failure that takes
> out your array.

This is true.

> >If it's not on tape, it's not backed up.
> I'll respectfully disagree with that. There are many options that
> constitute a backup, and hard disk *IS* one of them. It fulfills the
> criteria of :
> You can put data on it
> You can transport it offsite for storage
> You can read data back off it later
> The point I suspect you'd argue with would be the last point - can
> you still read data after <x> years and <y> journeys by carrier ?
> It's a valid point - and one where you need to take into account your
> requirements. Hard disks should be good for a few years, beyond that
> then you aren't talking backup - but archive which is a different
> matter. Even magtape has storage limitations - don't some outfits
> suggest you need to re-reel tapes every so often to avoid them
> becoming unreadable ?

They do indeed.  But I have DC600 cartridges from 1996 that read just fine;
we've gotten *much* better at coating over the years, and coercivities have
gone up enough that the bits are much less likely to fall off the tape
while you're (literally) not looking.

> In fact, there's an argument that archive shouldn't be on magnetic
> (or optical) media. Our oldest readable archives are all on more
> solid media like parchment and stone tablet ;-)

The archival standard for television program storage is color-separated
fine-grain black and white movie film.  Three reels of it.

> >It's not a backup unless you can make 2 of them, and carry one off
> >site.
> I have 4 sets, and keep the latest 2 off-site. Easy enough with hard
> disks, and takes a lot less space than the SLR-100 tapes I used to
> use. I got the SLR drive and a stack of tapes free, but it got to the
> point where home backups were taking days and it would have taken
> days to recover anything in the worst case where I'd have to
> recatalogue the media first.

And a story about the "Oracle Studs at Mass General" and their A/B switch 
to swap the mirror side of the RAID 1 on their Pick DB server so they could
rollback the logs and do a phase-coherent backup seems on point here...


though you'll have to scrool for it.

> >http://baylink.pitas.com/#747F
> A point I've made to people in the past - the fastest way to transfer
> data is a van load of disks/tapes/punched tape/whatever. But as
> online gamers will tell you, raw bandwidth isn't everything.

The original observation, about a station wagon full of 9-track to move 
Usenet traffic, is attributable, I believe, to Karl Kleinpaste, or Henry
Spencer, I can never remember which.  And yes, the latency is murder.

-- jra

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