Question 5400RPM HDD in NAS for streaming 4k videos

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velocci

velocci

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Dec 10, 2005
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Hi all, I have a Dlink DNS 323 nas which I want to store all my 4k .mkv movies so I can stream them on my HTPC. the nas is connected to my 100Mbps network. If I put a Western Digital Red 5400PRM HDD in there, would that cause any buffering/studdering? they guy at the store said 5400RPM vs 7200RPM wouldn't make a difference because the bottleneck is the 100Mbps network speed. Is this correct?
 
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velocci said:
I just realized they have 7200RPM WD red. So the extra RPM won't make any difference? Will it make any difference if I'm storing regular data?
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I have 4x 4TB Seagate Ironwolf (5900 RPM) in my QNAP NAS box.
It will make zero difference for movie playback or file storage.

I'm watching a movie right now, stored on the NAS, playing through the HTPC.
Not 4k, but that would work as well.
 
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velocci said:
So what is the point of making 7200rpm drives?
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Sequential read/write speeds in HDDs scale according to the data density. If you can write twice as much data per linear inch, then the sequential speed doubles. RPM affects it too, but to a much lesser extent (data density has increased over a thousand times in ~25 years, while RPM has only increased about 4x).

Random read/write speeds in HDDs scale according to RPM. The average random speed is limited by the time it takes to move the read/write head to a different section of the platter. On average, a "different" spot on the platter is a half rotation away. So you move the head to the proper track, and have to wait for the platter to rotate 180 degrees.

A 3600 RPM drive spins its platter 60x a second. So a half rotation takes 1/120 second. A 7200 RPM drive spins its platter 120x a second. So a half rotation takes 1/240 second. Its random speeds are 2x as fast as a 3600 RPM drive.

The bottleneck on HDDs are almost always the random read/write speeds. A good HDD could hit 150 MB/s sequential speeds. But its 4k random speeds were usually down near 1 to 1.5 MB/s (240 random sectors per second * 4096 bytes per sector is almost exactly 1 MB/s, and you could improve it a little more with NCQ, which rearranges random read order so nearer sections of the platter get read first). Before SSDs arrived, Increasing RPM was the only way to improve the random speeds.

For playing back movies, sequential speeds are what's important. So the RPM doesn't really matter (unless the drive is badly fragmented). Would be a different story if your application were, say, reading/writing hundreds of database transactions to the drive per second. Nowadays, anything that needs high random read/write speeds uses SSDs, so HDD RPM is kind of a moot point.

Edit: BTW, if I'm doing my math right, a 4k Blu-ray holds 75-100 GB of data. I dunno what bitrate they typically use, but if you figure it can hold a max 4 hour movie, then the average bitrate will be around 55 Mbps. Figure this can spike up to 80-100 Mbps during action sequences. So while it will work over your 100 Mbps network, any transient network glitch will cause a freeze or dropout. You would be advised to re-encode your 4k videos to something with a lower bitrate than raw Blu-ray. (100 Mbps = 12.5 MB/s, which is far below the 150-250 MB/s sequential speeds of modern HDDs.)
 
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ok so 7200 is no better than 5400PRM for my application. Let me ask another question, the guy at the store said the WD Red is 5400RPM so it doesn't produce as much heat which is what you want for a nas HDD cause its always on. so then why does WD also make a 7200RPM Red drive? is it cooled more than the 5400RPM drive?
 
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velocci said:
ok so 7200 is no better than 5400PRM for my application. Let me ask another question, the guy at the store said the WD Red is 5400RPM so it doesn't produce as much heat which is what you want for a nas HDD cause its always on. so then why does WD also make a 7200RPM Red drive? is it cooled more than the 5400RPM drive?
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A 'faster' drive probably generates a little bit more heat.
WD Red are built for being in close quarters in a NAS box. If he said it makes a difference, he's just blowing smoke.
 
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they are sata drives. what about copying large files from one of these 5400RPM red drive to another drive on the network. would 7200 RPM make the transfer faster? Assuming of course the other drive is 7200rpm or an SSD.
 
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velocci said:
they are sata drives. what about copying large files from one of these 5400RPM red drive to another drive on the network. would 7200 RPM make the transfer faster? Assuming of course the other drive is 7200rpm or an SSD.
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Performance relies on the slowest device in the chain.
Here, that would be the LAN.

For a NAS box in consumer use, don't stress over 5400 vs 5900 vs 7200.
 
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velocci said:
Hi all, I have a Dlink DNS 323 nas which I want to store all my 4k .mkv movies so I can stream them on my HTPC. the nas is connected to my 100Mbps network. If I put a Western Digital Red 5400PRM HDD in there, would that cause any buffering/studdering? they guy at the store said 5400RPM vs 7200RPM wouldn't make a difference because the bottleneck is the 100Mbps network speed. Is this correct?
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The DNS323 was an under powered NAS, and it pretty old. You should consider adding $150 to your budget to buy a new DS218J. You will be amazed how slow that DSN323 is compared to a new enclosure.
 
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