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From: Franc Zabkar on 6 Sep 2009 18:56
Looking at Table 1 on page 10 of the following document, I see that
the 1.5TB and 2.0TB drives both have 4 platters and 8 heads, and
identical data densities.

Barracuda LP Series SATA Product Manual:
http://www.seagate.com/staticfiles/support/disc/manuals/desktop/Barracuda%20LP/100564361b.pdf

In fact the only difference in the specs is the number of guaranteed
sectors.

Why wouldn't Seagate have used 3 platters and 6 heads?

I considered the possibility that, for the same capacity, more
platters means less cylinders, and therefore better average seek
times, but this isn't reflected in the specs.

Surely this isn't a yield issue?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
From: jj on 6 Sep 2009 21:04
Franc Zabkar wrote:

> Looking at Table 1 on page 10 of the following document,
> I see that the 1.5TB and 2.0TB drives both have 4 platters
> and 8 heads, and identical data densities.

Clearly the 1.5TB drives are actually drives with one non viable platter.

Thats the only way you can make those numbers fit, particularly the data densitys.

> Barracuda LP Series SATA Product Manual:
> http://www.seagate.com/staticfiles/support/disc/manuals/desktop/Barracuda%20LP/100564361b.pdf

> In fact the only difference in the specs is the number of guaranteed sectors.

Bet thats just not bothering to spell out the one non viable platter in the 1.5TB drives.

> Why wouldn't Seagate have used 3 platters and 6 heads?

Presumably because they cant get 2TB that way currently.

> I considered the possibility that, for the same capacity,
> more platters means less cylinders, and therefore better
> average seek times, but this isn't reflected in the specs.

> Surely this isn't a yield issue?

Bet it is.


From: Arno on 7 Sep 2009 09:34
Franc Zabkar <fzabkar(a)iinternode.on.net> wrote:
> Looking at Table 1 on page 10 of the following document, I see that
> the 1.5TB and 2.0TB drives both have 4 platters and 8 heads, and
> identical data densities.

> Barracuda LP Series SATA Product Manual:
> http://www.seagate.com/staticfiles/support/disc/manuals/desktop/Barracuda%20LP/100564361b.pdf

> In fact the only difference in the specs is the number of guaranteed
> sectors.

> Why wouldn't Seagate have used 3 platters and 6 heads?

> I considered the possibility that, for the same capacity, more
> platters means less cylinders, and therefore better average seek
> times, but this isn't reflected in the specs.

> Surely this isn't a yield issue?

Why not? The 1.5TB model may just be a way to not have to
scrap 2TB models that do not make the cut. Also, producing
2TB drives and limiting them to 1.5TB may be cheaper than
having two assembly lines for 1.5TB and 2TB both. Would
not be the first time...

Arno

From: Franc Zabkar on 9 Sep 2009 19:53
On 7 Sep 2009 13:34:33 GMT, Arno <me(a)privacy.net> put finger to
keyboard and composed:

>Franc Zabkar <fzabkar(a)iinternode.on.net> wrote:
>> Looking at Table 1 on page 10 of the following document, I see that
>> the 1.5TB and 2.0TB drives both have 4 platters and 8 heads, and
>> identical data densities.
>
>> Barracuda LP Series SATA Product Manual:
>> http://www.seagate.com/staticfiles/support/disc/manuals/desktop/Barracuda%20LP/100564361b.pdf
>
>> In fact the only difference in the specs is the number of guaranteed
>> sectors.
>
>> Why wouldn't Seagate have used 3 platters and 6 heads?
>
>> I considered the possibility that, for the same capacity, more
>> platters means less cylinders, and therefore better average seek
>> times, but this isn't reflected in the specs.
>
>> Surely this isn't a yield issue?
>
>Why not? The 1.5TB model may just be a way to not have to
>scrap 2TB models that do not make the cut. Also, producing
>2TB drives and limiting them to 1.5TB may be cheaper than
>having two assembly lines for 1.5TB and 2TB both. Would
>not be the first time...
>
>Arno

If Seagate is producing drives with 4 fully functional platters and
then turning off 2 heads, why not take full advantage of the potential
performance gains?

Reducing the number of cylinders instead of turning off an entire
platter would result in better average access times and higher average
throughput (because the outer cylinders pack more data per revolution
than the inner ones).

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
From: Arno on 9 Sep 2009 20:15
Franc Zabkar <fzabkar(a)iinternode.on.net> wrote:
> On 7 Sep 2009 13:34:33 GMT, Arno <me(a)privacy.net> put finger to
> keyboard and composed:

>>Franc Zabkar <fzabkar(a)iinternode.on.net> wrote:
>>> Looking at Table 1 on page 10 of the following document, I see that
>>> the 1.5TB and 2.0TB drives both have 4 platters and 8 heads, and
>>> identical data densities.
>>
>>> Barracuda LP Series SATA Product Manual:
>>> http://www.seagate.com/staticfiles/support/disc/manuals/desktop/Barracuda%20LP/100564361b.pdf
>>
>>> In fact the only difference in the specs is the number of guaranteed
>>> sectors.
>>
>>> Why wouldn't Seagate have used 3 platters and 6 heads?
>>
>>> I considered the possibility that, for the same capacity, more
>>> platters means less cylinders, and therefore better average seek
>>> times, but this isn't reflected in the specs.
>>
>>> Surely this isn't a yield issue?
>>
>>Why not? The 1.5TB model may just be a way to not have to
>>scrap 2TB models that do not make the cut. Also, producing
>>2TB drives and limiting them to 1.5TB may be cheaper than
>>having two assembly lines for 1.5TB and 2TB both. Would
>>not be the first time...
>>
>>Arno

> If Seagate is producing drives with 4 fully functional platters and
> then turning off 2 heads, why not take full advantage of the potential
> performance gains?

> Reducing the number of cylinders instead of turning off an entire
> platter would result in better average access times and higher average
> throughput (because the outer cylinders pack more data per revolution
> than the inner ones).

Because this would make the strategy obvious?
And in addition, there is the yield question.

Arno
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