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Old 09-05-2013, 11:42 AM   #1
BobCamp1
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Differences between AV hard drives and green drives

Since everyone is busy upgrading their Roamios, and this question came up in the previous thread, I'd like to address it in a separate thread. That way if this thread gets closed, at least the other thread can remain open.

I have actually worked at a company that makes hard drives, as an engineer. I can't publish the proprietary designs because I don't work there anymore. I could also get sued for divulging too much information. So I'm walking a tightrope here. If I'm too vague in some areas, it's because I'm in CYA mode.

In the very beginning (10 years ago), there was a difference between them. It had to do with thermal calibration. Normal drives would have to go offline for a few 100 ms to recalibrate themselves based on the temperature change in the hard drive. That obviously would be bad for a streaming application. But modern techniques make type of thermal calibration unnecessary. Modern drives can recalibrate for temperature on the fly.

Then there was a period where there was no difference between AV drives and green drives except profit margin and a longer warranty.

Before I left, they were actually developing different production lines for the two models of drives. Though mainly because they needed to add another green/AV line to keep up with demand for AV drives, and they just decided to make it a dedicated AV line to shift the AV demand off the other lines. So now there COULD be some differences between them mechanically, but I'm thinking the differences in hardware are trivial. All hard drives are designed more or less the same (except for the RPM and case height), and they all are designed (as best as possible) to run 24/7/365. No hard drive mfr. recommends powering down their hard drives a few hours a day to give them a rest. Even modern OSs are constantly doing some housecleaning, so a green hard drive will constantly be accessed whenever the PC is on.

The firmware differences were also subtle:

Acoustic mgmt: green set to normal, AV set to quiet.
ATAPI 7 streaming support: both had it, technical support provided and advertised only on AV drives. The AV drives had the latest bug fixes, while the green drives were a build or two behind but more stable. It seemed silly to intentionally disable that support in green drives -- it would have created more problems than benefits.

That's it for the differences. It turns out that most consumer PCs also want most of the AV drive features, including fancy read/write techniques to speed things up even more. Intel's RST is an example of this.

Regarding the streaming support (including the "don't report an error" feature), the commands for those are different than the typical hard drive commands. They are "extensions" in ATAPI 7 (and ver. 8). Download the spec. for free yourselves and try to stay awake reading them. You need substantial changes to the OS kernel and one or two levels up in the OS and the apps to support them. I left just before the MRDVRs became popular, but at the time I'm pretty sure no DVR was using those streaming extensions. We weren't getting any calls about those extensions, which was odd because we were pretty sure they didn't work that well and if anyone DID try to use them, they would have had problems and called us. But that might have changed since I left.

Besides, the Tivo kernel and its apps are available for download as well. You should be able to see if they are using those streaming extensions or not. I'll see if I can do that in my spare time, though I can't promise anything.

Regarding the whole "don't report errors" feature, we considered it very dangerous and totally useless. It gave too much control over our customers, who didn't know how hard drives worked. If an OS were truly tailored to an embedded DVR app, then it shouldn't freak out when an error is reported. What it should do is warn the user the hard drive is about to die. Errors occur all the time and are almost always corrected, but if the HD has trouble correcting the error that sector is normally moved from the bad spot to a good spot and not reported as bad to the OS. The hard drive only reports an error when it CAN"T correct the error or move the sector, which means the hard drive is circling the drain. I always thought DVR mfrs would use this feature to cover up defective hard drives and lower the amount of returns they would have.

Finally, I pulled the critical performance specs. from a WD Green drive and a WD AV-GP drive. This doesn't mean I used to work *there*, I chose these because they are used by a lot of people. I could also be comparing two generations of hard drives.

WD20EURS (AV) vs. WD20EZRX (Green)

Max. sustained transfer rate: 130 MB/s vs. 147 MB/s. The Green is FASTER. Note that one MPEG4 1080p stream only needs 22 Mbps, and one MPEG4 720p stream needs just 12 Mbps. So both are plenty fast enough.

Both have 64 MB cache.

Neither published their RPM speeds. Dead giveaway they are lower than 6000 RPM.

Max. power: 4.4 Watts vs. 4.1 Watts. The Green is actually a little cooler. It may be spinning a little slower.

Noise: 24 dBa vs. 27 dBa. The AV drive is a little quieter, though at those levels you won't hear anything more than 3 feet away.

Warranty: 3 years vs. 2 years.

Price: $99 vs. $96.

For the extra $3 and an additional one year warranty, I'd currently recommend the WD20EURS drive over the WD20EZRX for DVR and PC use. But I'd base my decision solely on those two factors. I also think the Green drive is a newer design than the AV drive -- it consumes less power AND it's faster.

Last edited by BobCamp1 : 09-06-2013 at 01:58 PM.
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Old 09-05-2013, 12:18 PM   #2
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Quote:
Originally Posted by BobCamp1 View Post
Max. sustained transfer rate: 130 Mb/s vs. 147 Mb/s. The Green is FASTER. Note that one MPEG4 1080p stream only needs 22 Mbps, and one MPEG4 720p stream needs just 12 Mbps.
You've got things mixed up here. The transfer rates are in megabytes per second. MPEG4 is measured in megabits per second. A factor of 8 difference there.
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Old 09-05-2013, 12:41 PM   #3
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I can definitely hear them at more than 3 feet away. I have a couple of the WD20EZRX drives. And just putting one in a drive caddy it's easy for me to hear. And I can hear the Romaio Pro or any TiVo from 15 feet away(in a quiet room). But I also hear those noises more easily than most people.
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Old 09-05-2013, 01:21 PM   #4
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I just installed a WD30EZRX into my Roamio Pro and I cant hear it at all. I have never used an AV drive yet in a TiVo
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Old 09-06-2013, 01:50 PM   #5
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You've got things mixed up here. The transfer rates are in megabytes per second. MPEG4 is measured in megabits per second. A factor of 8 difference there.
That's what that small voice in the back of my head was saying! I remember the drives could easily handle at least 20 video I/O streams but the math wasn't adding up! I changed my original post accordingly.

Last edited by BobCamp1 : 09-06-2013 at 01:59 PM.
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Old 09-06-2013, 01:55 PM   #6
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Originally Posted by aaronwt View Post
I can definitely hear them at more than 3 feet away. I have a couple of the WD20EZRX drives. And just putting one in a drive caddy it's easy for me to hear. And I can hear the Romaio Pro or any TiVo from 15 feet away(in a quiet room). But I also hear those noises more easily than most people.
I too am sensitive to this noise. Two big problems are motor vibration and the sound echoing around inside the metal case. I put my hard drive on a foam bump pad lying loose on the bottom of the PC, next to a case fan blowing air on it. I make sure not to cover up the vent holes on top (these are usually marked). The hard drive is counting on being bolted to something metal to keep it cool, but that ends up turning the entire case into a speaker. With my method, the hard drive runs a little warmer (good) but a lot quieter (better). Not only that, but if you unplug the fan, that's exactly how they're tested for noise.

Those noise values given in those datasheets are meaningless, but can be used relatively within the same mfr as a comparison. There are some quiet PC websites that do actual tests to determine how loud they really are. But it's going to vary based on how and what they're mounted.

Last edited by BobCamp1 : 09-06-2013 at 02:12 PM.
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Old 09-12-2013, 08:26 PM   #7
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Originally Posted by BobCamp1 View Post
...
WD20EURS (AV) vs. WD20EZRX (Green)
...
Max. power: 4.4 Watts vs. 4.1 Watts. The Green is actually a little cooler. It may be spinning a little slower.
I was given the impression the power difference was in part due to WD20EURS using 3x667GB platters and the WD20EZRX using 2x1TB platters. It is hard to figure out platter configuration with WD, but sometimes you can tell by comparing the listed weights in the specs. The WD20EZRX is lighter than the WD20EURS, but that could also be for other reasons. So the lower weight and lower power provide circumstantial (but not definitive) evidence of this theory.

There could even be platter variations within the same line. In that case, you need to look at the 6 digit code after the product #. Even then, if you start dealing with refurbs, it isn't guaranteed what you are getting. If they tell you anything, it only applies to original units.
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Old 09-12-2013, 09:10 PM   #8
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Bob, thanks for the info. I upgraded all my Premieres with green drives and always worried they weren't up to the job. Not worried about noise, just reliability. Makes me feel better.
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Old 09-03-2014, 07:27 AM   #9
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Came across this on the Seagate website, thought it might be of some interest. http://www.seagate.com/files/www-con...5-1-1403us.pdf
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Old 09-03-2014, 11:25 AM   #10
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I would think for a constantly running drive, you would want a Red or Black drive, especially if you are recording multiple shows and have more than one Mini. I realize the green drives are quieter, but the red drives are designed for NAS, which is basically what the tivo is acting as to the Minis.
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Old 09-03-2014, 11:40 AM   #11
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What drive does TiVo use currently in the Roamio? I know a number of you have upgraded...
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Old 09-03-2014, 12:24 PM   #12
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I really wouldn't think red or black would be good because of the possible heat they could generate, let alone possible noise or vibration, which might be a hindrance.
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Old 09-03-2014, 12:46 PM   #13
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What drive does TiVo use currently in the Roamio? I know a number of you have upgraded...
I created a thread a few days ago because I was curious as well and got some interesting results so far. http://www.tivocommunity.com/tivo-vb...d.php?t=520584

I'd love to make it a database reference listing all the different stock hard drives for the Premiere and Roamio (and future product) lines.

Last edited by JWhites : 09-03-2014 at 01:02 PM.
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