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 Post subject: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 11th, 2011, 19:35 
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Joined: April 11th, 2011, 12:52
Posts: 6
Location: Portugal
What are this Access times due to? Bad head in one of the face of the platters????

512byte-sector is enabled
The same happens when native 4K-sector "WD Advanced Format" is enabled
The bench in the pic is done right after a low level format pass using 512byte-sector mode
AAM is @ 256


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HDTune_Benchmark_AccessTime_WDC_WD20EARS-00MVWB0.png
HDTune_Benchmark_AccessTime_WDC_WD20EARS-00MVWB0.png [ 56.8 KiB | Viewed 2965 times ]
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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 11th, 2011, 19:40 
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Joined: April 11th, 2011, 12:52
Posts: 6
Location: Portugal
Now with AAM @ 128...

Any clues what is this condition...


The drive i brand new... Is it safe to keep it?


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File comment: Now with AAM at 128
HDTune_Benchmark_AccessTime_128AAM_WDC_WD20EARS-00MVWB0.png
HDTune_Benchmark_AccessTime_128AAM_WDC_WD20EARS-00MVWB0.png [ 57.34 KiB | Viewed 2963 times ]
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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 11th, 2011, 19:48 
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Joined: May 6th, 2008, 22:53
Posts: 2138
Location: England
AAM changes disk noise, by changing seek speed profile, so I'm not surprised at some change in the seek times. If you suspect a weak head, then don't look at the access time (i.e. predominantly seek time), look at read throughput benchmark instead.

What is the actual problem you are trying to solve? Or is it just that you have run a benchmark and are trying to understand a result, but there is no known problem?


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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 11th, 2011, 20:07 
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Joined: April 11th, 2011, 12:52
Posts: 6
Location: Portugal
Yep 2nd option... There is no actual problem.
The throughput is flawless besides the noticeable delay on the beginning of the disk due to the head unparking.

It works ok in 4K AF mode even in windows xp inside a usb enclosure (partition created with windwos 7, no need to use WD align software).
It generates a more heat when in 512byte-sector mode.

So...

Yes i am trying to understand the result, and; assess if it means problems in the future.
If it is a stable condition or if is going to be something that in the future can worsen and eventually lead to data loss.

I never saw that pattern nor in my drives nor in benchmarks found in the internet of this or any other drive.


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File comment: AAM @ 128
HDTune_Benchmark_128AAM_WDC_WD20EARS-00MVWB0.png
HDTune_Benchmark_128AAM_WDC_WD20EARS-00MVWB0.png [ 56.33 KiB | Viewed 2958 times ]
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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 11th, 2011, 20:19 
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Joined: April 11th, 2011, 12:52
Posts: 6
Location: Portugal
Any thoughts on these access times, anyone?


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File comment: With AAM @ 256
Native AF 4K mode enabled
Before LL Format (Note: LL format only possible with 512byte mode!!!)

HDTune_Benchmark_WDC_WD20EARS-00MVWB0 READ.png
HDTune_Benchmark_WDC_WD20EARS-00MVWB0 READ.png [ 75.81 KiB | Viewed 2956 times ]
File comment: With AAM @ 256
Native AF 4K mode enabled
Before LL Format (Note: LL format only possible with 512byte mode!!!)

HDTune_Benchmark_WDC_WD20EARS-00MVWB0 WRITE.png
HDTune_Benchmark_WDC_WD20EARS-00MVWB0 WRITE.png [ 75.83 KiB | Viewed 2956 times ]
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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 11th, 2011, 21:56 
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Joined: September 8th, 2009, 18:21
Posts: 9753
Location: Australia
As Vulcan said, AAM is not the issue here. Instead it appears that your drive has read problems that begin around the 800GB mark.

The main portion of the access time graph is good to about 800GB. The spread of data points is about 11msec, which is the latency of one full rotation at 5400 RPM. However, after this point it appears that about one quarter of the reads require one additional rotation, ie one additional read retry. I suspect that your drive has 2 platters and 4 heads, in which case it looks like one head is either faulty, or incorrectly calibrated. But I'm not a data recovery guy, so that's only speculation on my part.

_________________
A backup a day keeps DR away.


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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 12th, 2011, 21:12 
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Joined: May 6th, 2008, 22:53
Posts: 2138
Location: England
@RicardoNC:
RicardoNC wrote:
Bad head in one of the face of the platters????

Looking at the shape of the read throughput lines, I see no evidence to support that suggestion. All the graphs I have seen before where there is a weak head, include noticeable sharp and significant "dips" in the throughput - your graphs do not show such "dips". That is the part of your questions that I expected to be able to help with, and with your new throughput graphs, my analysis of your suggestion is as above. Here are a few more comments, but no answers...

I have no explanation for the interesting shape of the access time graphs - but that does not mean there is a fault. The fact that this drive model is sold as being "eco friendly" means I would not be surprised to see deliberate performance (seek) limitations being done, to reduce power consumption. As I understand your posts, your only evidence for there being a "problem", are these graphs. It is possible to sometimes discover what seems to be a "problem" - and later find out (after discussions with the manufacturer) that this was an undocumented & deliberate firmware behaviour, which caused specific effects on performance. That happened to me... My point is just that an unexpected observation or behaviour, does not necessarily mean a fault.

Unfortunately you are trying to prove a negative i.e. trying to check that your drive is OK, since you have no proof of a fault. That type of situation has big limitations. If someone does have the same model of drive and will run the same test for comparison, then their data would be interesting.

One final thought: If I was looking for any evidence of a problem with a disk, I would be looking at its full SMART data (my preferred utility is smartmontools, available in Windows & Linux versions), although interpreting that data is not an exact science. :) You may want to consider looking at that SMART data from this drive. If it shows no problems, then that is inconclusive (because not all problems can be seen in SMART data); however if it does show problems, then that evidence would be helpful to your investigation.

I hope you find the answers you are looking for. :)


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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 13th, 2011, 18:25 
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Joined: July 16th, 2008, 17:52
Posts: 486
Location: The Lab.
Green drives are designed to provide "decent" performance with as low power consumption as possible. I am not surprised to see pretty lackluster access times for these drives.

If you want performance, dish out some more money and go for a performance model drive, like a WD2002FAEX , or a WD2003FYYS if your are planning on using RAID.


Regards,


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 Post subject: Re: WD20EARS-00MVWB0 - What are this Access times due to?
PostPosted: April 14th, 2011, 0:34 
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Joined: April 11th, 2011, 12:52
Posts: 6
Location: Portugal
Thanks

This drive is ok for the use I need, which is external drive fit into a Revoltec Alubook 2. For now it is on the desktop, with 7 installed and it just gave me boot time under 30 sec after installing intel inf drivers, and that pretty good stuff around here.


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