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 Post subject: Hitachi DeskStar: Difference in access speed per platter?
PostPosted: October 21st, 2015, 14:04 
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Joined: September 17th, 2012, 13:42
Posts: 61
Location: Europe
As this is (thank goodness) nothing about a broken drive for a change (in fact, HDD Sentinel now reports a 100% Health after a good thorough format on sector level (previously 97%)), I thought I might put it into the Lounge instead.

Code:
Model: HDT725050VLAT80
Size: 500 GB
Total LBA: 976,773,168
DCO: <Factory reset>
This is really interesting, even though I only noticed it by accident as I have other things to do than watching Victoria's "Defectoscop" running all day ;)

Up to approx. LBA 601,95x,xxx Victoria reported millions of sectors accessed at 5 ms and only a marginal number of sectors accessed at 20 ms. That means, up to this LBA, the drive might approach the performance of an (old) SATA I drive. Wow!

When it reached the 602,1xx,xxx LBA, there was a significant change: all of a sudden, the 5 ms and 20 ms reads went in PARALLEL! And there was way more light gray spots in the graphics. In short, the drive performance was quite a tad SLOWER, also visually perceptible by the sector count for the '20 ms' line reaching several thousand in no time.

Could it be one of the platters (the 3rd and last perhaps?) starts at around LBA 602-million?
That would be logical to me. Other platters have full speed, with only marginally needing 20 ms access time.
But the platter where LBA 602-million and higher are located, obviously performs slower than the other platters.
Supposing that there are 3 platters in total, that would mean P#1 holding 300m LBAs, P#2 holding 300m LBAs, and finally P#3 holding nearly 377m LBAs.
However, this is only a vague assumption; but who would try to open that fully-working drive just to verify a claim?! :P


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 Post subject: Re: Hitachi DeskStar: Difference in access speed per platter
PostPosted: October 21st, 2015, 14:19 
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Joined: April 3rd, 2011, 0:19
Posts: 2003
Location: Providence, RI
No, data is striped across all platters similar to a RAID array. Samsung have the longest runs between switching heads, but even then it's usually only a few Gb of data before it jumps to another head.

It is normal to see slower results in the higher LBA ranges as it's reading data closer to the spindle and the diameter of the track is smaller. Therefore there is less physical platter (and thus less sectors) passing under the read/write head in each rotation so it's physically limiting how fast it can read sectors.

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 Post subject: Re: Hitachi DeskStar: Difference in access speed per platter
PostPosted: October 21st, 2015, 14:30 
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Joined: September 17th, 2012, 13:42
Posts: 61
Location: Europe
Thanks for the reply.
data-medics wrote:
It is normal to see slower results in the higher LBA ranges as it's reading data closer to the spindle and the diameter of the track is smaller.

I guessed so! BUT ... I didn't assume that the reading speed slowdown would be that abruptly, as if one had flipped a switch! The tool is running under real DOS, but I could record the "moment of suspense" with my phone (well, if someone asks me to do that) and I assure you, it really looks interesting how it "turns off turbo mode" all of a sudden! :)


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