Shortstroked WD5001AALS-00E3A0 Caviar Black 500GB

  • Thread starter Thread starter Franc Zabkar
  • Start date Start date
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Franc Zabkar

A Western Digital user recently suggested that his 500GB
WD5001AALS-00E3A0 Caviar Black drive may have been fitted with two
500GB platters which had been shortstroked:

http://www.tomshardware.com/forum/f...rint=0&numreponse=0&quote_only=0&new=0&nojs=0

He reports that his "benchmark read/write from HDtune shows maximum
read/writes as 129MB/sec and minimum as 97MB".

http://i54.tinypic.com/1zlr9f5.png

AISI, the subject drive's maximum transfer rate of ~130 MB/s is
consistent with a 500GB platter density. The number of zones also
appears halved, suggesting that the drive has indeed been
shortstroked.

Other WD5001AALS models (eg WD5001AALS-00L3B2) appear to have 2
platters with densities of 250GB per platter. My understanding is that
the data transfer rate increases with the square root of the platter
density.

Hence ...

data rate (00L3B2) / data rate (00E3A0) = sqrt (250GB / 500GB)

ie data rate (00L3B2) = 130 x sqrt (0.5) = 92 MB/s

This is consistent with the benchmark results.

I also believe that the subject drive may have only 3 active heads,
not 4. I say this because its performance graph shows 9 zones. The
performance graphs for drives with a full complement of 18 or 19 zones
indicate that the 9th zone ends at about the 64% capacity point. If
the subject drive has a capacity of 250GB per head, then ...

3 x 250 x .64 = 480GB

.... which would tend to confirm that only 3 heads are in use.

The only question I have is, if the drive is shortstroked, why isn't
its seek time significantly lower?

Here are several HD Tune read benchmark graphs:

WD5001AALS-00E3A0 - 129MB/s max, 97 MB/s min, 11.0ms access, 8 or 9
zones:
http://i54.tinypic.com/1zlr9f5.png

WD5001AALS-00E3A0 - 136MB/s max, 99 MB/s min, 12.1ms access, 9 zones:
http://s001.radikal.ru/i193/1007/b2/b9e907d1985f.jpg

WD5001AALS-00L3B2 - 92MB/s max, 44 MB/s min, 12.2ms access, 19 zones:
http://i77.photobucket.com/albums/j63/euro-kid/HDTune_Benchmark_WDC_WD5001AALS-00L.png

WD5001AALS-00L3B2 - 92MB/s max, 44 MB/s min, 12.3ms access, 19 zones:
http://www.overclock.net/attachment...ts-hdtune_benchmark_wdc_wd5001aals-00l3b2.png

WD5001AALS-00L3B - 97MB/s max, 44 MB/s min, 12.5ms access:
http://dyski.cdrinfo.pl/benchmark/hdtune/hdtune-832-85758-154.png

WD5001AALS-00L3B - 92MB/s max, 45 MB/s min (est), 12.6ms access, 18 or
19 zones:
http://www.uppicweb.com/x/i/iy/90dhd.jpg


- Franc Zabkar
 
Franc Zabkar said:
A Western Digital user recently suggested that his 500GB
WD5001AALS-00E3A0 Caviar Black drive may have been fitted with two
500GB platters which had been shortstroked:

He reports that his "benchmark read/write from HDtune shows maximum
read/writes as 129MB/sec and minimum as 97MB".

AISI, the subject drive's maximum transfer rate of ~130 MB/s is
consistent with a 500GB platter density. The number of zones also
appears halved, suggesting that the drive has indeed been
shortstroked.
Click to expand...
Other WD5001AALS models (eg WD5001AALS-00L3B2) appear to have 2
platters with densities of 250GB per platter. My understanding is that
the data transfer rate increases with the square root of the platter
density.
Click to expand...
Hence ...
Click to expand...
data rate (00L3B2) / data rate (00E3A0) = sqrt (250GB / 500GB)
Click to expand...
ie data rate (00L3B2) = 130 x sqrt (0.5) = 92 MB/s
Click to expand...
This is consistent with the benchmark results.
Click to expand...
I also believe that the subject drive may have only 3 active heads,
not 4. I say this because its performance graph shows 9 zones. The
performance graphs for drives with a full complement of 18 or 19 zones
indicate that the 9th zone ends at about the 64% capacity point. If
the subject drive has a capacity of 250GB per head, then ...
Click to expand...
3 x 250 x .64 = 480GB
Click to expand...
... which would tend to confirm that only 3 heads are in use.
Click to expand...
The only question I have is, if the drive is shortstroked, why isn't
its seek time significantly lower?
Click to expand...

Seek time is only weakly dependent on the seek distance. Sure,
track-to-track is faster than full stroke, but half-stroke is not
that much faster than full-stroke.

Arno
 
Seek time is only weakly dependent on the seek distance. Sure,
track-to-track is faster than full stroke, but half-stroke is not
that much faster than full-stroke.
Click to expand...

Here is the benchmark graph for a "full stroke" drive:
http://i77.photobucket.com/albums/j63/euro-kid/HDTune_Benchmark_WDC_WD5001AALS-00L.png

If you extrapolate the bottom of the access time graph, the
full-stroke time is about 16 msec.

The half-stroke point would be where the transfer rate is half way
between the min (44MB/s) and max (92MB/s) values, ie somewhere between
the 65% and 70% mark. The access time at this point is between 12 and
12.5 msec. This is near enough to the same figure that we measure for
the "full-stroke" of the short-stroked drive.

- Franc Zabkar
 
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