Seagate ST32000542AS & ST31500541AS -- specs

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/s...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.

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/s...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.

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.

Barracuda LP Series SATA Product Manual:
http://www.seagate.com/staticfiles/s...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

On 7 Sep 2009 13:34:33 GMT, Arno put finger to
keyboard and composed:

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.

Barracuda LP Series SATA Product Manual:
http://www.seagate.com/staticfiles/s...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.

Franc Zabkar wrote:
On 7 Sep 2009 13:34:33 GMT, Arno put finger to
keyboard and composed:

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.

Barracuda LP Series SATA Product Manual:
http://www.seagate.com/staticfiles/s...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

Franc Zabkar wrote:
On 7 Sep 2009 13:34:33 GMT, Arno put finger to
keyboard and composed:

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.

Barracuda LP Series SATA Product Manual:
http://www.seagate.com/staticfiles/s...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?

Because its a lot harder to do and that particular market is entirely driven by price.

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).

And is a lot harder to do than just not using a couple of heads on the less than ideal platter.

On 10 Sep 2009 00:15:31 GMT, Arno put finger to
keyboard and composed:

Franc Zabkar wrote:

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.

I was wondering how WD's Raptor drives were achieving 8ms access times
while their other models were getting only 14ms:
http://www.hdtune.com/testresults.html#Western_Digital

It seems that WD's 10K RPM drives had smaller 3.0" platters compared
with the usual 3.25":
http://forums.macrumors.com/archive/.../t-200923.html

My calculations (for Fujitsu drives) suggest that the usable data area
occupies a band of width 2.37 cm:
http://groups.google.com/group/micro...3?dmode=source

Assuming the reduced platter size results in a reduction of 6mm in the
usable radius, then that equates to about 73%. That, and the reduced
rotational latency, explains the faster access times.

So, if WD got away with it, why couldn't Seagate? ;-)

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Franc Zabkar wrote:
On 10 Sep 2009 00:15:31 GMT, Arno put finger to
keyboard and composed:

Franc Zabkar wrote:

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.

I was wondering how WD's Raptor drives were achieving 8ms access times
while their other models were getting only 14ms:
http://www.hdtune.com/testresults.html#Western_Digital

It seems that WD's 10K RPM drives had smaller 3.0" platters compared
with the usual 3.25":
http://forums.macrumors.com/archive/.../t-200923.html

My calculations (for Fujitsu drives) suggest that the usable data area
occupies a band of width 2.37 cm:
http://groups.google.com/group/micro...3?dmode=source

Assuming the reduced platter size results in a reduction of 6mm in the
usable radius, then that equates to about 73%. That, and the reduced
rotational latency, explains the faster access times.

So, if WD got away with it, why couldn't Seagate? ;-)

WD is (or used to be) the only HDD company without SCSI drives.
Seagate does this in their SCSI models and you pay for it.

Arno