[mythtv-users] Multiple directories

Michael T. Dean mtdean at thirdcontact.com
Wed Nov 21 10:06:40 UTC 2007


On 11/21/2007 03:29 AM, f-myth-users at media.mit.edu wrote:
>     > From: "Michael T. Dean"
>
>     > On 11/20/2007 06:27 AM, Nicolas Will wrote:
>     > >      4. mv /var/lib/mythtv/recordings/* /srv/mythtv/recordings
>
>     > Too bad this one takes so long.  Perhaps once hard drives get
>     > unreasonably large (i.e. Seagate is aiming for 300TB drives by
>
> 300Tb, not 300TB, e.g., around 30TB, and I'll bet the first 2010
> drives are more like 5-6TB.  There are many misquotes floating
> around of a -single- article which seems to have zero independent
> verification (though no doubt there are better-sourced figures in
> the trade press).  A factor of 30 over the next 3 years is already
> enormously larger than the rate at which capacities have been
> increasing over the last decade (even given GMR!); a factor of
> 300 seems unlikely.
>
> [Do a search for ``seagate HAMR'' for more info.  The idea's been
> kicking around for at least 5 years (I recall papers in various APS
> journals); the basic principle is to get around the superparamagnetic
> limit by spot-heating of the medium w/a laser, presumably (I assume;
> it's been a while since I've read about it) to decrease the coercivity
> of the medium by getting it closer to its Curie temperature.  This is
> very reminiscent to me of certain magneto-optical storage systems from
> the early 90's; I even have such a drive sitting on a shelf behind me
> (though I haven't spun it in years; its capacity was 1GB, back when
> 1GB of hard disk was a 5 1/4" device that cost $10K, one of which is
> sitting on that very same shelf).]

I don't see how the 300TB could be incorrect.

Hitachi's 1TB HDD has 5 platters at 200GB/platter using an areal density
of 140Gb/in^2.  So, 200GB/platter at 140Gb/in^2 means 11.111in^2 per
platter (in a 3.5" HDD).

Seagate has a 250GB/platter technology that uses an areal density of
180Gb/in^2 (
http://www.seagate.com/ww/v/index.jsp?locale=en-US&name=null&vgnextoid=9292a41246303110VgnVCM100000f5ee0a0aRCRD
).  (They haven't rolled out any 1.25TB, 5-platter drives, yet, as they
seem to be concentrating on lower-noise/-power drives with the tech for
now, but they are using this technology in their 3-platter 750GB
HDD's.)  And 250GB/platter at 180Gb/in^2 means 11.111in^2 per platter. 
So, based on numbers from 2 different manufacturers matching up, I'm
going to take this as the size of a platter.

Seagate, themselves, said (
http://www.seagate.com/ww/v/index.jsp?locale=en-US&name=Seagate_Swings_%22HAMR%22_To_Increase_Disc_Drive_Densities_By_A_Factor_Of_100&vgnextoid=46e18adc5448d010VgnVCM100000dd04090aRCRD
), "HAMR, combined with self-ordered magnetic arrays of iron-platinum
particles, is expected to break through the so-called superparamagnetic
limit of magnetic recording by more than a factor of 100 to ultimately
deliver storage densities as great as 50 terabits per square inch."

50Tb/in^2 * 11.1in^2 = 555.56 Tb/platter or just under 70TB/platter (or
55.556TB/platter at 10b/B).  Stick 5 platters in a 3.5" drive, and it
looks like you could easily fit 300TB in the drive.

In other words, a change from current areal densities of ~140-180Gb/in^2
to the "expected" 50Tb/in^2 density is a factor of about 300--not a
factor of 30.

So, is the Seagate press release the "-single- article which seems to
have zero independent verification" that was misquoted?  Is my (5:00am)
math wrong?  Are there some other factors that make it possible to use
only one platter per drive and to get only about 1/2 the usable area per
platter with HAMR?  Or are you saying that Seagate is expecting more
like 5Tb/in^2 from first-generation HAMR drives and that we won't see
50Tb/in^2 for a long time?

Regardless, it seems that a 300TB HDD will--at some time--be possible
using the technology that Seagate is hoping to roll out in 2010-2012
timeframe.  And, even at 30TB on a single drive, few "real people" (i.e.
not including enterprises or Myth users ;) currently have a need for
significantly more space, meaning that HDD manufacturers would have to
find other factors on which to compete.  I'm hoping the next will be
performance.

The rest of the info you provided is very interesting.  I agree that the
interface has improved, but not significantly so (perhaps mainly because
of the lack of a need due to the inability to dramatically increase
read/write speed).  I also agree that much needs to change to really
improve read/write speed, but I'm all for those changes (whatever they
may be)--I really don't care how my data is stored, as long as it is
stored.  I'd just like for it to be stored (and read) much more quickly.

Mike


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