Check hard disk motor speed


#1

Hi,

is there any possibility to check rotation speed of hard disk? My WD Caviar Black (WD6402AAEX) has slower transfer rate than other (106MB/s vs. 133MB/s). Spinup time value in SMART is also lower (3825 vs. 4300 vs. 4266 (WD1002FAEX)).

Thank you.


#2

I don’t know of any utility that claims to measure the rotation rate. Maybe someone else could help you with that. However, I believe those utilities that report the RPM simply do so by looking at the 512-byte data block returned by the drive in response to an ATA Identify Device command.

See section 7.16.4 (page 131 of PDF) of the following document.

Working Draft AT Attachment 8 - ATA/ATAPI Command Set (ATA8-ACS):
http://www.t13.org/Documents/UploadedDocuments/docs2008/D1699r6a-ATA8-ACS.pdf

Word 217 reports the “Nominal media rotation rate”.

In this example …

http://www.users.on.net/~fzabkar/HDD/ST32000542AS/9XW0CXE1.TXT

… the RPM is 0x170C, which is 5900 RPM.

http://www.google.com/search?q=0x170C+in+decimal

One way you could estimate the RPM is by examining the spread of data points in the graph of access time in HD Tune’s read benchmark.

For example, in the following graph you can see that, at the 450GB mark, the band of data points are about 8 msec wide.

http://i38.tinypic.com/axxxcz.png%5b/IMG

The total access time is the time required to seek to the target cylinder, plus the time required for the target sector to pass under the read/write head. The latter time component can vary from 0 to one full revolution. Therefore this “rotational latency” will be seen as a band whose width is 8.33 ms in the case of a 7200 RPM drive, and about 11ms for a 5400 RPM drive.


#3

Thank you for your reply.

None of the utilities are not able to read this parameter. For example: HD tune - Rotation speed: - ; Crystal Disk Info - Rotation rate: Unknown; It’s the same for all SATA 6Gb WD blacks, which I have. But I’m afraid that “Nominal media rotation rate” is not real rotation speed…

I suspect that rotation speed is only slightly lower (for example, 200 RPM lower - 7000 RPM). And this is not reflected in the graph, it’s very low value for that graph…

But, thank you. I think I’ll have to write directly to WD. I think it’s also in their interest. Slow Black drive is not a good thing…


#4

If the rotation speed were 7000 RPM, say, then the data rate would be reduced to …

133 x (7000 / 7200) = 129 MB/s

Looking at it the other way, if rotation speed were to be responsible for the slower transfer rate, then …

speed = 7200 x (106 / 133) = 5738 RPM

Clearly neither explanation is consistent with your observations.


#5

Hmm, that’s true. I should have first calculate it…

I did some tests. According to the chart, it seems that rotation speed is fine. But it’s strange. I do not understand why it is so much slower. I attach the graphs for both drives. 

WD6402AAEX (older and faster drive) read benchmark result:

WD6402AAEX (newer and slower drive) read benchmark result:


#6

In your other thread I suggested that the difference may be a consequence of differing platter densities:

http://community.wdc.com/t5/Desktop/WD6402AAEX-new-drive-slower-than-older-drive/m-p/39315#M2116

BTW, I can’t see your graphs. I believe it takes some time for images to be approved.


#7

Thank you. I replied there.