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Hard Drive Performance - How do you really tell?

Posted on 2012-03-19
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I build servers for video surveillance. The servers stream live video data to one drive (A), then a few times a day archive the data to a different drive (B). The specs call for a high performance model for drive A and a lower performance higher capacity drive for drive B.

I use Western Digital Drives so this is about their options. Is anyone able to summarize and answer the following:

1.      Which is the higher performance drive and what benefits/drawback each will have in my particular use? (Storage size is not relevant)

                                 RPM      Buffer       Interface      Avg Latency      Transfer Rate
        WD2503ABYX      7200      64MB      3Gb/s            4.2ms            128MB/s

Versus

      WD1500HLHX      10000      32MB      6Gb/s            3.0ms            145 or 128 – (not sure)

Versus

      WD2003FYYS      7200      64MB      3Gb/s            4.2ms            138MB/s

2.      Is Transfer rate the most important spec?

3.      What does an A/V designation really offer over a ‘Black’ drive for example

4.      How important are seek times & latency in my application?

Thanks,
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Question by:bselltiz
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by:John Hurst
ID: 37740340
The servers I specify for my clients all use 15,000-rpm drives. 10,000-rpm might be ok, but I think 7,200-rpm would be slow.

Assuming the range of available drives is all modern by today's standards, faster is always better in my opinion. ... Thinkpads_User
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by:bselltiz
ID: 37740383
15K drives are not an option for this. Server's may have been the wrong classification, lets just say workstations :->
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by:John Hurst
ID: 37740395
For workstations, use 10,000-rpm drives if they are available. I use a 7200-rpm drive in my laptop only because faster hard drives do not appear to be available. I also have 7200-rpm drives isn my desktop, but it is just a general purpose machine. You can get 10,000 rpm drives for workstations and should do so for performance.

... Thinkpads_User
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by:bselltiz
ID: 37740409
Thanks for the tip.

Maybe someone else can give me a more in depth answer to the question as stated above?
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by:John Hurst
ID: 37740430
Your own chart above shows a decent comparison, which is why I did not comment further. The faster drive has shorter latency (by a lot) and faster transfer rates. That is why I like them.

.... Thinkpads_User
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by:bselltiz
ID: 37740444
The WD2003FYYS is 7200 and has a higher transfer rate
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by:John Hurst
ID: 37740451
I used the 145 figure for the 10,000rpm. Also, the 10,000rpm drive gets to the data much faster.

I had two equal XP systems running on two drives which converting from one drive to the new one. The old drive was 5,400-rpm; the new drive was 7,200-rpm. XP on the old drive was like rowing through molasses. That was 5 years ago or more. I have only used 7,200-rpm drives in my laptops since.

As soon as a foolproof 500Gb SSD drive comes out (may not be in my lifetime) or a 10,000-rpm laptop drive comes out, I will get one.

... Thinkpads_User
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by:bselltiz
ID: 37740458
Gotcha. So you are saying that transfer rate is most important?  I am guessing that for transfer rates to increase you need more RPM and a higher interface speed?

And then next important would be latency and seek times which relate to the RPM of the drive?
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by:John Hurst
ID: 37740464
I think latency and seek are more important than transfer rate. Notice how the faster drive performs better on latency, but the transfer rates for all three are fairly close together.

... Thinkpads_User
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by:bselltiz
ID: 37740487
I have read that streaming video has different requirements than regular computing but haven't been able to correlate that statement into what the specific demands are. hence all the specifics above. Thanks man.
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by:BigSchmuh
ID: 37741508
It's all a matter of io usages.
ONE video stream stored on a drive will act as a sequential write io throughput...and I would buy a 5400 rpm drive to lower my energy cost about this.
...but you have a different usage every day when transferring the video stream to the other drives. Anyway, a good filecopy function should not really lower more than 50% of your raw performance if it allows for a good cache memory use.

Theoretically, you video streams can be evaluated as below:
Video (and audio) bitrate x #Streams = RAW io throughput ... a 720p stream with a good quality need about 5Mbps bitrate which is less than 1MB/s throughput
5400 rpm means 90 rotations per seconde which is 90 head moves per second at most
160MB/s sequential (read or write) means the head does NOT seek for another place (it slowly move following the next sectors list)...which is about 1.7MB/rotation at full speed
All head seek requires some time to reach the right position...avg is half a rotation which means you are at most lowering by 50% your instant throughput
Optimizing your throughput means enlarging your io size to lower the head seek needs...using 128KB io (or larger), you may sustain up to 66%->75% of your HDD sequential announced throughput (about 120MB/s in this case)
Many ways to "enlarge" ios...using a hw raid card (use the highest stripe available) with a large write cache backed by a battery...using an application that is aware of this requirements and handle a write cache that allows to build large io buckets
==> So, theoretically, you can have about 120x 720p streams in parallel on a 5400 rpm drive but you should lower this hope by half to allow your backup streams and by half again to ensure you have enough storage bandwidth not to loose a single frame.
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by:bselltiz
ID: 37741836
That is very in depth information, thank you very much.

Would it be possible for you to address each of my 4 questions above each individually? I would really appreciate it.

Thanks
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BigSchmuh earned 500 total points
ID: 37743548
0/ The specs call for a high performance model for drive A and a lower performance higher capacity drive for drive B.
It looks like this is not a program that you can control the io usage of...so it may not be optimized ("enlarge ios") to send many video streams to a storage subsystem

1/ Drive comparison
WD2003FYYS may be the best performer for your usage because of a slightly higher sequential throughput.
...but if the program does not aggregate the video streams before sending them to the storage subsys, then the fastest rpm drive WD1500HLHX 10krpm may win the challenge.

2/ YES...if the program handles this obvious "enlarge ios" optimization

3/ A/V designation...means a different warranty
To my opinion, this is only a marketing and warranty difference...

4/ You app relies on an OS and it may poorly optimized...which leads you to some io requirements dedicated to the OS...mainly random io.
Random io depends on seek time and latency, the fastest rpm is the best performer.
Most servers now boot on a RAID 1 SSD (no rotation at all and overkilling IOPS performance) or iSCSI (network raw drive that allows sharing storage resources and driveless servers )
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