WD6402AAEX new drive slower than older drive


I have 3 640GB black edition drives. Two WD6402AAEX and one WD6401AALS. One of WD6402AAEX (the new one - bought recently) is slower than the other (and also slower than WD6401AALS).

For example, HD tune read test (same settings, same SATA III port, same system, same firmware):

  1. WD6401AALS - maximum read speed: 116MB/s

  2. WD6402AAEX (the “old” one - SN: WCATR060xxxx) - maximum read speed: 133MB/s

  3. WD6402AAEX (the “new” one - SN: WCATR202xxxx) - maximum read speed: 106MB/s

WD6402AAEX Performance Specifications:

 Transfer Rate (Buffer To Disk): 126 MB/s (Max)

Any suggestions? Note: Local vendor tested for me another WD6402AAEX with same poor result.

Thank you.

I believe the differences in data transfer rates are due to differences in platter densities. AFAICT, 133 MB/s, 116 MB/s, and 106 MB/s are the data rates you would expect from 500GB, 400GB, and 333/320GB platters. Since all three drives have a capacity of 640GB, ISTM that the higher speed drives are not using their full capacity. In this case, it could be that they have been “short stroked”. This would show up as faster access times. Could you upload the HD Tune graphs to a file sharing site?

To make sense of the performance data, let’s assume that, if a drive has four times the data density (bits per square inch) as another drive, then it would have twice as many tracks per inch, and twice as many bits per inch (or sectors per track).

The data rate is …

(sectors / track) x (bytes / sector) x (rotations per second)

This means that …

rate_A / rate_B = sqrt( density_A / density_B )

So, comparing the “old” WD6402AAEX with the “new” one, we have …

rate_A / rate_B = 106 / 133 = 0.797

sqrt( density_A / density_B ) = sqrt (320 / 500) = 0.80

The above results would tend to confirm that the “new” drives have the older, lower density platters.

Can you post the DCM (Drive Configuration Matrix) for each drive? Dates of manufacture? Any other distinguishing data on the label or PCB?

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Thank you for your reply. Sorry that I did not answer. I did not get a message that the answer came.

Yes, it makes sense. But it is the same model, same firmware.

Here are the graphs:

WD6402AAEX (old)

WD6402AAEX (new)

New WD6402AAEX:


Date: 22 JUN 2010

Old WD6402AAEX:


Date: 22 MAR 2010

I found this:

1- Motor (same)
2- Base (same)
3- Latch (different)
4- Bottom VCM (different)
5- Media (different)
6- Headstack (same)
7- Actuator-Preamp (same)
8- Top VCM (same)
9- Separator (same)

I suppose the media is platter. So it seems that WD sells for the same money worse drive…

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