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Re: large scale (audio) file I/O on OS X : help or insight requested
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Re: large scale (audio) file I/O on OS X : help or insight requested


  • Subject: Re: large scale (audio) file I/O on OS X : help or insight requested
  • From: Paul Davis <email@hidden>
  • Date: Wed, 11 Mar 2015 22:26:10 -0500

The math all looks good. Unfortunately, Robin's test is not indicative of the correct use case. I suspect most people would be OK with the idea that you can only handle about 50 tracks on an external USB2 drive. The harder results to explain come from internal drives. I will definitely get my own mac mini with a spinner inside running tomorrow and re-run the test there with your additional line, and then redo the math you just did above. We know by existence proof (aka Logic) that the system can handle 128 or more tracks.

On Wed, Mar 11, 2015 at 10:08 PM, Hamilton Feltman <email@hidden> wrote:

> On Mar 11, 2015, at 6:53 PM, Paul Davis <email@hidden> wrote:
>
> robin reports back that your dd-tester gives:
>
>  41.1806 MB/sec write
>  42.6064 MB/sec read
>
> (Western Digital 6400AAV - we can't find specs online)
>
> He also tried it formatted as FAT32, with essentially no change in the results.
>

Ok, this is enough information to calculate if your drive is performing within spec. Looking at the first example (block size 65536)

From your test:
$ ./run-readtest.sh -f 10 -d /Volumes/OSXext/disktest/ 65536 131072 4096000
# Building files for test...
# Blocksize 65536
# Min: 8.9910 MB/sec Avg: 9.4645 MB/sec  || Max: 0.890 sec
# Max Track count: 51 @ 48000SPS
# Sus Track count: 49 @ 48000SPS
65536 8.9910 9.4645 0.8898 0.00912

So:
 file size: 10485760
 num files: 128
 total bytes: 1342177280
 seeks = 1342177280 / 65536
 seeks: 20480
 total_time: 270.484

Drive reports:
 42.6064 MB/sec read (44676048 bytes/sec)
 Time required to stream 1342177280 bytes -> 30.04 seconds

Blocksize 65536
Number of seeks 20480
Time taken: 270.484 seconds
Time available for seeks: 270.484 - 30.04 = 240.444 seconds
240.444 / 20480 -> 11.74 ms seek time

Out of 270 seconds it took to read the 1.25GB, the drive had to spend 240 seconds performing 20480 seeks, with an average seek time of 11.74 milliseconds.
This drive seems to be performing well.

Regards,
Hamilton


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References: 
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Hamilton Feltman <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Paul Davis <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Hamilton Feltman <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Paul Davis <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Hamilton Feltman <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Paul Davis <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Hamilton Feltman <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Paul Davis <email@hidden>)
 >Re: large scale (audio) file I/O on OS X : help or insight requested (From: Hamilton Feltman <email@hidden>)

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